They started equal. Jerry spent 1 unit, Ben spent 2 units (twice as much). Since both began with the same amount, the difference in what is LEFT equals the difference in what was SPENT = 1 unit.

Jerryspentleft $18Benssleft $5

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

  1. Difference left → $18 − $5 = $13
  2. This equals the extra unit Ben spent → 1 unit = $13 (Jerry spent $13, Ben spent $26)
  3. Each at first → Jerry spent + Jerry left = $13 + $18 = $31

Each of them had $31 at first.

Check: Ben $31−$26=$5, Jerry $31−$13=$18, and $26 = 2 × $13. ✓