Question

Your friend is 1.2 times taller than you. Your friend is 64.5 inches tall. How tall are you?

Answer 1

You are X, if your friend is 1.2 times taller than you= 1.2X
That's why 64.5=1.2X
                   X=53.75
But you should write 53.8 inches tall. Because there is one number after point.
As a result, you are 53.8 inches tall

Answer 2

You have to divide your friends weigh by 1.2 to get  the result. : if you were 1.2 times taller than they, you would multiply, so the oppisite is dividing!

so  it will be 64.5/1.2=53.75.