Book 1 was $12.50 and book 2 was $15.00 so 13.00 +15.00 = $28.00
He was buying 4 books, so these 2 were 25% off so 28.00 * .25 = $7.00
These two books came out to 28-7 = $<<28-7=21.00>>21.00
Books 3 & 4 were both $10 each so 2*10 = $20.00
When you add all 4 books together, 21+20 = $<<21+20=41.00>>41.00
To get free shipping he would need to spend 50-41 = $<<50-41=9.00>>9.00 more on books
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