(4x + 5y)² - 5x(16/5*x + 6y) = 16x² + 40xy + 25y² - 16x² - 30xy = 10xy + 25y²

x=√8=2√2

y=√2

10*2√2*√2 + 25*(√2)² = 10*2*2 + 25*2 = 40+50 = 90

Verified answer

(16x^2 + 40xy + 25y^2) - 16 - 30xy =

16x^2 + 10xy + 25y^2 - 16 = 16*8 + 10√2√8 + 25*2 - 16=

128 + 10√16 + 34 = 162 + 10*4 = 202