See, pls, the attached picture, the area determined by the conditions marked by yellow lines.
Solve 10x = 4.1 for x. Divide both sides of this equation by 10: x = 4.1 / 10.
x = 0.41
5a(b-c)=d. Here, we are trying to isolate the variable b.
Divide both sides by 5a: b-c=d/(5a)
Add c to both sides: b=
Missing check = $412.20 - $331.60 = $80.6
Hope it helps!