Answer:
The answer to your question is: $61
Explanation:
Data
Book 1 = 60% that costs $18
Book 2 = 30% that costs $21
Process
Book 1
60% ----------------- $18
100 % ---------------- x
x = (100x 18)/60 = $30 actual cost
He needs to save 30 -18 = $12
Book 2
30% ------------------ $21
100% ----------------- x
x = (100 x 21) / 30 = $70 is the actual cost
He needs to save 70 - 21 = $49
Total
$49 + $12 = $61 needs to save to buy two books