You seem to be saying that Y=4/X+SQRT X +0.2 -5X, and that x is given as 4/5. To evaluate Y=4/X+SQRT X +0.2 -5X, replace each occurrence of x with 4/5:
y = 4 / (4/5) + sqrt(4/5) + 0.2 - 5(4/5)
= 5 + 2 / sqrt(5) + 0.2 - 4
Can you simplify this further?