a - 1.2b = - 3 ⇒ eq. 1
0.2b + 0.6a = 12 ⇒ eq. 2
a - 1.2b = - 3
a = 1.2b - 3 ⇒ eq. 3
Substitute eq. 3 to eq. 2
0.2b + 0.6(1.2b - 3) = 12
0.2b + .72b - 1.8 = 12
Combine like terms
0.92b = 12 + 1.8
0.92b = 13.8 ⇒ divide both sides by 0.92 to get the value of b
b = 15
Substitute the value of b to eq. 3
a = 1.2b - 3
a = 1.2(15) - 3
a = 15
to check: substitute the values of a and b to:
eq. 1
a - 1.2b = - 3
15 - (1.2)(15) = -3
15 - 18 = - 3
- 3 = -3 ⇒ correct!
eq. 2
0.2b + 0.6a = 12
(0.2)(15) + (0.6)(15) = 12
3 + 9 = 12
12 = 12 ⇒ correct!
