EXPLANATION
Given the system of equation:
(1) e + f = 48
(2) e = 3f
Substituting e=3f into e + f=48:
3f + f = 48
Adding similar terms:
4f = 48
Dividing both sides by 4:
f = 48/4
Simplifying:
f = 12
Replacing f=12 in e + f =48
e + 12 = 48
Subtracting -12 to both sides:
e = 48 - 12
e = 36
Answer: There has been sold 12 items of f and 36 items of e.
