Let's count how much we spent:
Now we take away this amount from the initial budget:
So he has $20 total
Friday: 20 - 4.58 = $15.42 left
Saturday: 15.42 - 7.43 = $7.99 left
Sunday: 7.99 - 3.50 = $4.49 left
He has $4.49 left.
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