In trigonometry, the hypotenuse is always the longest side but, the adjacent and opposite sides are not as consistent. When and how do you know which is side is the adjacent vs. opposite in a right triangle? In this diagram, when is seven on the opposite side? When does it become adjacent?
You might know that sin(x) , cos(x) and tan(x) are what's known as trigonometric functions. FUNCTIONS , and as what's common with any function f(x), they have an argument , which is the value you replace x with, and thus get an output, with respect to the provided input.
Similarly, these trigonometric functions are blind to the triangle you are applying them to, they are simply providing an output with respect to the argument you provide it. You might have learnt the "soh cah toa" as a trick to remember what ratios they represent, so applying this to your triangle, if I feed the argument B to tan(x) , it will spit out a certain value, which will be equal to the ratio represented tan(19°); that will be 'opposite to B' divided by 'adjacent to B'. (Opposite side to an angle is the side not connected to it, and since hypotenuse remains fixed, adjacent side is the last of the three)
What you have done seems to be correct, except that x=7cot(19°).