1) na + nb + 5a + 5b = n(a+b)+ 5(a+b) = (a+b)(n+5)
2) 7x - 7y + bx -by = 7(x-y) +b(x-y)= (x-y)(7+b)
3) 10a - by + 10b - ay= 10(a+b) - y(b+a)= (a+b)(10-y)
4) pq - x - px + q = q(p+1) -x(1+p) = (p+1)(q-x)
5) b - a - ab + 1 = -a(1+b)+(b+1) = (1+b)(-a+1)
6) 2cx - cy - 6x + 3y = c(2x-y) - 3(2x+y) =(2x+y)(c-3)
7) 15ax - 14by + 10bx - 21ay = 3a(5x-7y) + 2b(5x-7y) = (5x-7y)(3a+2b)
8) 56pq -1 - 7q + 8p = 8p(7q+1) - (1+7q) = (7q+1)(8p-1)