We have a piecewise-defined function. This means a function broken into pieces.
f(-3) pertains to the upper piece of f(x), where x is LESS THAN 0.
So, f(-3) = -3.
Now f(0) pertains to the bottom piece because x = 0.
f(0) = 8(0) + 5
f(0) = 5.
Lastly, f(9) pertains to the bottom piece because 9 is greater than 0.
f(9) = 8(9) + 5
f(9) = 72 + 5 or 77
Did you follow?