The bag is one unit (= the wallet) plus an extra $70. Together they make $180.

Wallet?Bag?$70$180

Plain numbers are given; italic underlined numbers are worked out.

  1. 2 units + $70 → $180
  2. 2 units → $180 − $70 = $110
  3. 1 unit (wallet) → $110 ÷ 2 = $55
  4. Bag → $55 + $70 = $125

The bag costs $125.

Check: $125 + $55 = $180, and $125 − $55 = $70. ✓