I need help im taking a test and i dont get this

You are at a restaurant and owe $38 for your meal. you want to leave a 20% tip. how much will your tip be?

Alcoa was $10.02 a share yesterday. today it is at $9.75 a share. if you own 50 shares, did ou have capital gain or loss ? how much of a gain or loss did you have ? express the capital gain/loss as a percent of the original price

Gabrielle's age is two times mikhail's age. the sum of their ages is 84. what is mikhail's age?