Isaac was 51cm when he was born. When he was 10, he had grown in length by 174% how tall was he?
Use your terms carefully. Consider that growth of 50% give a result 1.5 as big as the starting value. So, growth of 174% gives a result 2.74 times as big.
51 * 2.74 = 139.74 cm
Make sure that's how you intended to phrase the question.