Answer:
John gave Fred $48
Explanation:
Let
x be the amount of dollars John gave fred
y1 be the amount of dollars Fred has at the end
y2 be the amount of dollars John has at the end
Fred has
y1 = - $12 + x
John has
y2 = $84 - x
y1 = y2
- $12 + x = $84 - x
2*x = $96
x = $48