A+B+D=255 B+15=A D+12=B A=

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A+B+D=255 B+15=A D+12=B A=

1. A + B + D = 255
2. B + 15 = A
3. D + 12 = B
4. A = ?
5. Rearrange (3) to solve for D by subtracting 12 from each side: D = B - 12

Substitute (2) and (5) into 1
(B + 15) + B + (B - 12) = 255

Combine like terms:
3B + 3 = 255

Using our equation solver, b = 84

Substitute b = 84 into equation (2):
A = 84 + 15
A = 99