The ratio of Terry’s height to his uncle’s height is   : 

Multiply each part of the ratio by a same number of 20 to make them whole numbers:

 :  = ( × 20) : ( × 20) = 15:36

Then, divide each whole number of the ratio by common factors to find its simplest form:

15:36 = (15 ÷ 3) : (36 ÷ 3) = 5:12