Answer:
21
Explanation:
I shall change the pictures to letters
a + a + b = 40 --(1)
b - c = 7 --(2)
c + a = 19 --(3)
a - c + b = ?
From (1):
2a + b = 40
b = 40 - 2a --(4)
From (2):
b = 7 + c --(5)
Sub (4) into (5):
40 - 2a = 7 + c
c = 33 - 2a --(6)
Sub (6) into (3):
33 - 2a + a = 19
a = 14
Sub a = 14 into (4) and (6):
b = 40 - 2(14) = 12
c = 33 - 2(14) = 5
therefore, a - c + b = 14 - 5 + 12 = 21
Topic: simultaneous equations
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