Question

If 3a + 2b = 7 and 2a + 2b = 9 , what is the value of 5a+4b?

Answer 1

3a+2b=7→(1)

2a+2b=9→(2)

Subtract (2) from (1)

3a+2b-(2a+2b)=7-(9)

3a+2b-2a-2b=7-9

a=-2

Substitute a=-2 in equation(2)

2(-2)+2b=9

-4+2b=9

2b=13

∴a=-2 and 2b=13

Substitute a=-2 and 2b=13 in 5a+4b

5a+4b

⇒5a+2(2b)

⇒5(-2)+2(13)

⇒-10+26

⇒16

PLZ CHECK IF IT'S CORRECT  :)

Answer 2

A simple method for only this problem is to add up both the equations.

3a+2a+2b+2b=9+7

5a+4b=16

Hope you have understood.