7a - 4b
Step-by-step explanation:
Add the numbers ending with 'a' together, and then add the numbers ending with 'b' together.
First of all, I will put the letters beside each other.
2a + 5a + 3b - 7b
2a + 5a = 7a
3b - 7b = - 4b
Therefore, the answer is 7a - 4b.
