Final answer:
To make 'a' the subject of the formula 'a + 13 = 3b', you subtract 13 from both sides of the equation. The final formula then becomes 'a = 3b - 13'.
Step-by-step explanation:
To make 'a' the subject of the formula a + 13 = 3b, we need to isolate 'a' on one side of the equation. This can be achieved by subtracting '13' from both sides of the equation. Now the equation becomes:
a = 3b - 13
This is your final formula with 'a' as the subject. It's a fundamental step in learning algebra to be able to rearrange equations, and that's what was done here.
Learn more about Rearranging Equations