Answer: 5 Months
Explanation:
Alright, we know he will make $120 a month (since 50 + 70 = 120)
(Let's have months=m)
So now we need to figure out for how many months (m) will he need to get to $600.
We know 120 a month so we can get the equation: 120m=600
Now all we have to do is solve for m
Divide both sides by two to get m=5
Checking Answers
70(5)=350
50(5)=250
250+350=600
So this solution works.