4.
[tex]a) \ 4(x+3)-(2x-y) = 4x+12-2x+y =2x+y+12\\\\dla \ \ x = 3, \ \ y = -4\\\\2x+y+12 = 2\cdot3 + (-4)+12 = 6-4+12 = 14[/tex]
[tex]b) \ -8(-5x-3y+2)+9x^{2}-(7y-2) = 40x+24y-16+9x^{2}-7y+2=\\\\=9x^{2}+40x+17y-14\\\\\\dla \ \ x = 3, \ \ y = -4\\\\9x^{2}+40x+17y-14 = 9\cdot3^{2}+40\cdot3+17\cdot(-4) -14 =9\cdot9+120-68-14=\\\\=81+38 = 119[/tex]