Just look at the $18$-degree triangle for a minute.
You know one angle and one leg of that triangle.
Use those facts and your knowledge of trigonometry to write the length
of the other leg.
Now look at the $14$-degree triangle.
Again, you know one angle and one leg.
Write the length of the other leg.
The "other leg" of the $18$-degree triangle and the
"other leg" of the $14$-degree triangle
lie end-to-end along the same line (see the figure).
That is, they are two pieces of a single line segment.
Write a formula for the length of that segment.
The same segment is $35$ feet long according to the figure.
So this is equal to your formula.
Write the equation.
Solve the equation.
Remember there is only one variable in it,
so you just need to solve for that variable.