I have been struggling at this please help

21

Step-by-step 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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y=mx+b is the final answer!   : )