Question

A+B=140
A+C=77
B+C=105

qual o valor de A?

Answer 1

A + C = 77
C = 77 - A

B + C = 105
B = 105 - C
B = 105 - (77 - A)
B = 105 - 77 + A
B = 28 + A

A + B = 140
A + 28 + A = 140
2A = 140 - 28
2A = 112
A = 112/2
A = 56