Final answer:
To solve the equation a + b = 50 when a = 30, substitute the value of a and simplify the equation to find b = 20 as the solution.
Step-by-step explanation:
The correct solution of the equation a + b = 50 when a = 30 is found by substituting the value of a into the equation. This step looks like:
30 + b = 50.
To find the value of b, we subtract 30 from both sides of the equation:
b = 50 - 30,
b = 20.
Therefore, the correct solution is b = 20.