To solve for у, we can rewrite the equation as у = 212 - 124 = 88.

To solve for a, we can rewrite the equation as a + 458 = 345. Subtracting 458 from both sides gives us a = 345 - 458 = -113.

To solve for d, we can rewrite the equation as 2046 - d = 1398. Subtracting 1398 from both sides gives us d = 2046 - 1398 = 648.