Mandy told bill that she has read 16 books this year and reads 2 books each month. bill wants to catch up to mandy. he tracks his book reading with a table on his door. using his table below, what month will bill have read the same amount of books as mandy?
month books
may 4
june 8
july 12

We need to write equation for both mandy and bill on how many books they read depending on how many months passed.

Mandy's equation:
16 + 2x

she starts with 16 read books and she reads 2 books each month which is in total 2*x where x is number of months

Bill's equation:
4x
because from table we can see he is reading 4 new books each month.

now we need to make those 2 equations equal to eachother and solve for x because we want to see after how many months both will read the same that is why we set them equal.

16 + 2x = 4x
16 = 2x
x = 8

That means that in december he will catch her (if i counted months correctly :) )