What is the sum (0.40x+0.625) + (0.20x-0.25) ?

To add something like this, combine your like terms, meaning any term in the expression can be combined as long as they have the same variables and are raised to the same power. Knowing this, you would combine these values:

(0.40x+0.20x) + (0.625-0.25)

When simplified, you will result with this answer:

0.60x+0.375