18/30 = divide top and bottom by 6 = 3/5
second part we take 3/5 and multiply it by anything overitself because anything over itself is 1 and multiplying by 1 doesnt change anything..
EG..
3/5 x 3/3 (3 divided by 3 is 1 your really multiplying by 1)
3/5 x 5/5
3/5 x 10/10
3/5 x 589654/589654 its all the same long as its divided by itself