I double checked and it's 6.75 in decimals which you will learn how to convert in yr 6

I'm in year six and here is how ya do it
1 5/4 is an improper fraction (top heavy)so we convert it to 2 1/4 by seeing how many times the denominator goes into the numerator.
2 10/4 is also improper so that would become 4 2/4 by using the same method as before
So the answer is 4 and 1/2 add 2 and 1/4 which is
6 1/3

GOD IM IN 4TH

3 15/4 = 12 3/4
There
Ik my math
Btw I'm in 5th

Idk