To find f(-8), we substitute -8 into the function f(r) = -2r + 2z. In this case, we assume z is a constant or zero since it is not specified. The calculation proceeds as follows: First, we replace r with -8 in the function, resulting in f(-8) = -2(-8) + 2z. Next, we calculate -2 times -8, which equals 16, and then add 2z. If we assume z is 0, then f(-8) simplifies to 16. However, if z is not specified, we cannot determine the exact value of f(-8) without knowing z. Therefore, if z is assumed to be 0, the final answer is -144.