5a + 2a = 3

To solve the equation \(5a + 2a = 3\):

1. Combine the like terms on the left side:
   \(5a + 2a = 7a\).

So, the equation becomes: \[ 7a = 3. \]

2. Now, to solve for \(a\), divide both sides by \(7\): \[ a = \frac{3}{7}. \]

Therefore, the solution is: \[ a = \frac{3}{7}. \]