I got these answers right on the practice SAT but can not figure out how to do them properly. Some of them I got right because I guess or just plugged them in. Any help would be wonderful.

1) If which of the following must be true. The answer is But how? q.14-423

2) If what is the value of X? The answer is but how, do you use log or something? q.9-397

3) The graph above shows Elina's height in inches from age 6 to 12. Elina's height at the age of 12 was what percent higher than her height at the age of 6? Her height at the age of 6 was 45 inches and her height at the age of 12 was 60 inches. The answer is %. But how? q.15-399

All your help will be wholly and greatly appreciated.