Fie X suma de bani a Sofiei. Atunci :
[(X × 3 - 5 ) ×2 -4 ] - 1/4 × [(X ×3 -5) ×2 -4] -3 = 99
[( X ×3 -5) ×2 -4] × ( 1- 1/4) = 102
[( X ×3- 5 )× 2-4 ] × 3/4 = 102
[( X ×3 -5) ×2 -4] = 4×102 / 3
( X × 3 - 5) × 2 - 4 = 136
(X × 3 - 5) × 2 = 140
X × 3 - 5 = 70
X × 3 = 75
X = 25