Final answer:
The value of 'a' that would make the equation have infinitely many solutions is 26.
Step-by-step explanation:
The equation 123 + 24 = 121 + a can have infinitely many solutions if the value of 'a' is equal to the difference between the two sides of the equation. In this case, the difference between the left side (147) and the right side (121) is 26. So, 'a' would be 26.