Well the first thing when adding or subtracting a decimal is they need to have the same denominator (also known as the bottom number) because EX. you can not add 3/2( another way this can be written is 1 1/2 or 1.5) and 3/4 ( 0.75) because the bottom number is different.
Step 1. Make the bottom numbers the same
EX. in 3/2 + 3/4 how can you turn a 2 into a 4? Multiply it by 2! 2×2=4!
Step 2. Remember! what ever you do to the top you must do to the bottom!
EX. 3/2 + 3/4
3×2/ 2×2 = 6/4
6/4 + 3/4 = 9/4 (or 2 and 1/4)