Mia is three years older than twice her sister Brooke's age. The sum of their ages is less than 30. What is the greatest age Brooke could be?

Lets say Mia is represented by M and Brook is represented by B.

M=3xB

M+B=30

then you can plug it in to solve for B if M=3xB you can replace M in the bottom question with that

3B+B=30

4B=30

divide both by 4 to solve for B

B=7.5

Plug in your answer to check to be sure both sides are equal

3x7.5+7.5=30

30=30

So brook is 7 and 1/2

Mia is 3xB

7.5x3=30