1) (0.9*5 + 5*0.6) - (0.7*2 + 3*0.7) = 5*(0.9+0.6) - 0.7*(2+3) = 5*1.5 - 0.7*5 = 5*(1.5-0.7) = 5*0.8=4
2) (13*2.5 - 2.5*9) + (8*5.6 - 3.1*8) = 2.5*(13-9) + 8*(5.6-3.1) = 2.5*4 + 8*2.5 = 2.5*(4+8) = 2.5*12 = 30
3) (3.61*7 + 7*1.3) - (2.26*4 + 3*2.26) = 7*(3.61+1.3) - 2.26*(4+3) = 7*4.91 - 2.26*7 = 7*(4.91-2.26) = 18.55