Hello! I can help you!
a. The triangles are similar, because if we look closely and know a bit about parts and fractions, 24 is only 3/4 of 32, meaning that 24 is 25% smaller than 32. The side lengths are proportional and are similar in size.
b. Okay. Just by doing a bit of mental math and if you know a bit about finding a fraction of something, 3/4 of 28 is 21. We can set up an equation like this: 3x + 6 = 21. Subtract 6 from both sides to get 3x = 15. Divide each side by 3 to isolate the "x". 15/3 is 5. There. x = 5.