Multiply:
(1) 3x by 4y
(2) 2y by 4y
(3) 8a by 4m
(4) −4x by 8x
(5) −5a by −8b
(6) −6p by 4pq
(7) 2a2 by 5a2
(8) 3x2b2 by 5x
(9) −7m2n2 by 4m
(10) −5a2b by −7ab2