13 minus quarter of a number is equal to 15 less than the same number”
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х - is a number.

x/4 - is quarter of a number.

x - (13 - x/4) = 15

x - 13 + x/4 = 15

x + x/4 = 15 + 13

4x/4 + x/4 = 28

5x/4 = 28

x = 28•4/5

x = 22,4

Verification

13 - 22,4/4 + 15 = 13 - 5,6 + 15 = 22,4