If the name of the function is pay, wtih nickname p, and the variable is the numbers of hours of training, then the expression for 20 hours of payment is pay (20) or p(20).
In this case pay or p is the dependent variable and hours is the independent variable.
The area of a triangle is the height multiplied by the base divided by 2. Since this is a right triangle, you can simply use the two legs for this. The area of this triangle is therefore: