Despite the description specifying this is in a more matured classroom than most people I've taught, the question and tags are more general, so I decided it would be best to include this answer for people who hope for a solution that's less specific.
Advanced mathematics is inherently harder than simpler mathematics to create problems with, but this is how I create questions
In this example, I want to teach year 7 students algebra in a way that makes it look as simple as a preschool problem.
The first step is to determine a theme: in this case, simple objects in a preschool setting
Then, I must think of how algebra relates to simple objects. When substituting, you look at the total amount, a variable, and a way to create a difference between the total amount and variable (actually, I could exclude this, but define x if x=1 is kinda sad for a year 7 class). Maybe the variable and difference can use simple objects.
I must then create a purely mathematical expression or equation, along with a question for solving.
Find x where x+3=5,
Finally, I merge the two into a problem.
A person has 5 simple objects, if she has 3 simple objects of one type, and the rest are of another, how many of the second type of simple objects are there?
Now, we have a problem, and we can apply the theme. We find the things that are common between simple objects and preschool, and use that to change the wording.
A person has 5 fruits, if 3 are apples and the rest are oranges, how many oranges are there?
Add a few finishing touches, generally details to make the question more interesting and to confuse the students who have been too lazy to read it carefully.
Sally has 5 fruits in a basket, if 3 are apples and the rest are oranges, how many oranges are in the basket?
If you get a student who says "There's one basket, Mr!", you know who needs to brush up on their reading skills. I've had peers who read questions incorrectly a while back, and the results are hilarious, so I deliberately add these extra details.
It may sound simple to most when I say it, but I've seen people get stumped on creating simple things like this until I lead them through it. It's important to note my example was deliberately easy, it's extremely helpful to consciously think through this process with math past year 10 education.
Sorry in advance if the formatting is terrible, the iPad stack exchange app doesn't seem to have special mathematics formatting tools.