Respuesta :

Let

x -----> number of gallons of a 50% antifreeze

we have that

0.50(x)+0.15(90)=0.40(x+90)

Solve for x

0.50x+13.5=0.40x+36

0.50x-0.40x=36-13.5

0.10x=22.5

x=225

therefore

The answer is 225 gallons of a 50% antifreeze