They started equal. Martha spent $21 more than Mary ($36 vs $15), so after spending Mary has $21 more than Martha. Mary now = 2 units, Martha now = 1 unit, so that extra unit is the $21.<br><br>[[model:questions/solutions/q4154.png]]<br><br>• Extra spent by Martha → $36 − $15 = $21<br>• Mary − Martha now = 1 unit → $21 (so Martha now = $21, Mary now = $42)<br>• Mary at first → $42 + $15 = $57<br>• Both started equal → total = 2 × $57 = $114<br><br>They had $114 altogether at first.<br>Check: each $57; Mary $57−$15=$42, Martha $57−$36=$21, and $42 = 2 × $21. ✓<br><br>Alternative method (algebra):<br>• Let each start with $m. Mary: m − 15; Martha: m − 36.<br>• m − 15 = 2(m − 36)  ⇒  m − 15 = 2m − 72  ⇒  m = 57.<br>• Altogether at first = 2 × 57 = $114.