Olivia is 4 feet 10 inches tall. she compared her height with her younger sister, susan, and found that susan is 15 inches shorter than she is.
what is olivia's height, in inches?

what is susan's height, in centimeters?
1 inch=2.54 centimeters

A foot (or feet) is 12 inches.This means Olivia is four lots of 12 inches tall plus another 10 inches.Four lots of 12 is 48(4x12=48).48+10=58.
However Susan is 15 inches shorter than Olivia so Susan is basically Olivia's height minus 15 inches. Olivia's height, as we know, is 58 inches.
58 inches minus 15 is 43, therefore Susan is 43 inches tall. This means Susan's height equals 43 lots of 1 inch. Because 1 inch equals 2.54 centimeters, Susan's height equals 43 lots of 2.54 centimeters. To work this out without a calculator you could get rid of the decimal place and do 43x254=10922. Then, because the number that had the decimal point in had 2 digits after it(2 numbers) you add the decimal place back in 2 places from the right of your answer. In this case, it gives you 109.22. Therefore:
~Olivia's height: 58 inches
~Susan's height: 109.22 centimeters

I hope that helps you and I understand that it's a really long answer but I wasn't sure which bit you couldn't understand. :)