Finding missing factors (multiplication)

Match the addition problem to its correct multiplication problem
_____ x 4 = 16
4 x ______ = 16
7 x ____ = 21
_____ x 3 = 21
6 x _____ = 30
4 x _____ = 32
4 x _____ = 28
9 x _____ = 54
____ x 8 = 24
____ x 3 = 24
9 x ____ = 45
8 x ____ = 56
_____ x 7 = 63
_____ x 8 = 72
12 x ____ = 48
____ x 3 = 36
_____ x 6 = 72
9 x ____ = 81
9 x ____ = 90
_____ x 7 = 49