Equilateral triangles

We have $a$ number of $A$ tiles and $b$ number of $B$ tiles. We know that $a+b=25$ ( $a, b$ are integers).

We covered the equilateral below with these tiles.

Find the sum of all the possible values of $a$ .

Note : The area of the big equilateral triangle is $100$ , and both of the $A$ and $B$ tiles have an area of $4$ .