If your doing distributive property would u add like terns?

Jenisey has $24 to spend on seven pencils. after buying them she had $10. how much did each pencil cost.?

The first-serve percentage of a tennis player in a match is normally distributed with a standard deviation of 4.3%. if a sample of 15 random matches of the player is taken, the mean first-serve percentage is found to be 26.4%. what is the margin of error of the sample mean? a. 0.086% b. 0.533% c. 1.11% d. 2.22%

What is the best way to answer questions with a x expression in the question. for example 3x + 10x=?