Substitute the given values in the expression:
9y/x + z²-w = 9(4)/3 + 8² - 5
Simplify by performing multiplication and addition inside the parentheses first, then the exponentiation, and finally the division:
= 12 + 64 - 5
= 71
Therefore, 9y/x + z²-w = 71 when w=5, x=3, y=4, and z=8.