C. -45
These types of problems can be fairly simply once you understand substitution. Substitution is when we put in values (in this case -9 and 5) in their set variable (x and y in this case.)
The problem states that x=-9 therefore we put in -9 for x in the multiplication of xy so it looks like this: (-9)(y). Next we want to substitute in the y value which is 5 so that we now have (-9)(5).
Because there is no plus or minus sign, along with a division sign, we then MULTIPLY these two numbers because the variables are connected so -9*5 would equal to -45.
