Question

how to equate a=3-c and a= -2c​

Answer 1

let a=3-c (1)

and a=-2c (2)

putting the value of a from equation (2) in equation (1) we get.

-2c=3-c

-2c+c=3

-c=3 → c= -3

a=3-(-3)=3+3=6

Answer 2

a = 3 - c ...(i)

a = -2c ...(ii)

by equation (i) and (ii)

3 - c = - 2c

3 = - 2c + c

3 = - c

c = - 3