Respuesta :

inpus 0.8 for y
4x+8(0.8)=40
4x+6.4=40
minus 6.4 both sides
4x=33.6
divie both sides by 5
x=8.4

x=8.4 when y=0.8
4x+8y=40
4x + (8x.8)= 40
4x + 6.4 = 40 
4x = 33.6
x = 8.4