J = Jennifer's coffee powder at first
M = Mie's coffee powder at first
Jennifer had 3 times as much coffee powder as Mie at first, means:
J = 3 M
After Jennifer gives 16.77 kg to Mie Jennifer has J - 16.77 kg of coffee powder.
Mie has M + 16.77 kg of coffee powder.
Now Jennifer had 77.5 kg more coffee powder than Mie, this means:
J - 16.77 = M + 16.77 + 77.5
J - 16.77 = M + 94.27
Add 16.77 to both sides
J = M + 111.04
Replace J by 3M in this equation.
3 M = M + 111.04
Subtract M to both sides.
2 M = 111.04
M = 111.04 / 2
M = 55.52
At first Mie have 55.52 kg coffee powder.
Check result.
At first Jennifer have 3 M = 3 ∙ 55.52 = 166.56 kg coffee powder
After Jennifer gives 16.77 kg to Mie Jennifer has 166.56 - 16.77 = 149.79 kg of coffee powder.
Mie has 55.52 + 16.77 = 72.29 kg of coffee powder.
Jennifer's coffee powder - Mie's coffee powder = 149.79 - 72.29 = 77.5 kg
Jennifer had 77.5 kg more coffee powder than Mie.