Question

Show me how to do this equation

3e+4f= 28. - e - 3f =-18

Answer 1

Solve the system
3e + 4f = 28
- e - 3f = -18

Use substitution. From the second equation:
-e - 3f = -18 => e + 3f = 18 => e = 18 - 3f.

Substitute into the first:
3(18 - 3f) + 4f = 28
54 - 9f + 4f = 28
54 - 5f = 28
-5f = -26
f = 26/5 = 5.2

Then e = 18 - 3f = 18 - 3·(26/5) = 90/5 - 78/5 = 12/5 = 2.4.

Solution: e = 12/5, f = 26/5 (or e = 2.4, f = 5.2). Checked: both equations hold.