The ordered pairs (1, 81), (2, 100), (3, 121), (4, 144), and (5, 169) represent a function. what is a rule that represents this function?

What I see is that the number is being multiplied by itself.
Although I'm probably wrong, you lead off with the equation of f(x)=(x+8)^2
for examples, 1+8=9^2=81
2+8=10^2=100
3+8=11^2=121
4+8=12^2=144
5+8=13^2=169

The answer would be $68.04