1).
(5376 - a) - 3877 = 999
5376 - a - 3877 = 999
5376 - 3877 - 999 = a
a = 1499 - 999
a = 500
2).
(x - 7756) - 12000 = 4896
x = 4896 + 7756 + 12000
x = 24652
3).
4284 - (x - 378) = 1287
4284 - x + 378 = 1287
4284 + 378 - 1287 = x
x = 3375
1).
(5376 - a) - 3877 = 999
5376 - a - 3877 = 999
5376 - 3877 - 999 = a
a = 1499 - 999
a = 500
2).
(x - 7756) - 12000 = 4896
x = 4896 + 7756 + 12000
x = 24652
3).
4284 - (x - 378) = 1287
4284 - x + 378 = 1287
4284 + 378 - 1287 = x
x = 3375