Question 287018
Let x = the amount of 3% money
Then (15000-x) = the amount fo 4% money.
Interest = Principal * rate * time.

0.03x + 0.04x(15000-x) = 550
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0.03x + 600 - 0.04x = 550
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-0.01x = -50
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x = 5000 the amount of 3% money.
Therefore, 15000 - 5000 = 10000 the amount of 4% money.

Proof:
5000 * 3% = 150
10000 * 4% = 400, sums to 550.