Hey there!
Let's call this "number" x. We want four times the sum of this number and 15 to equal at least 120.
Therefore, we want this number times four plus fifteen to be greater than or equal to 120. We have:
Distribute:
Subtract:
Divide:
Your answer is C.
Hope this helps!
Find factors of 12 and 21
Divide 3 from both numerator and denominator.
(12/21)/(3/3) = 4/7
4/7 is your ratio equivalent to 12/21
hope this helps