2,4(3х+5у)-4у при 0,9х+у=2
при 0,9х+у=2:
2.4(3x+5y)-4y=2.4*3x+2.4*5y-4y=7.2x+12y-4y=7.2x+8y=8(0.9x+y)=8*2=16