Question

What is the sum of 1.57 and 6.88?

Answer 1

"Sum of" means addition of so take 1.57 + 6.88 and you get the sum which is 8.45

Answer 2

 What is the sum of 1.57 and 6.88?

Ok, so lets work this out together!

Sum means add.

   6.88
+ 1.57

That would be: 

= 8.45

Hope i helped!