Adults = 1 unit, girls = 3 units. Boys are 120 fewer than girls, so boys = 3 units − 120. The three groups total 846.<br><br>[[model:questions/solutions/q4146.png]]<br><br>• Adults + Girls + Boys = 1 + 3 + 3 units − 120 = 7 units − 120 → 846<br>• 7 units → 846 + 120 = 966<br>• 1 unit → 966 ÷ 7 = 138 (adults)<br>• Boys → 3 × 138 − 120 = 414 − 120 = 294<br>• Difference boys − adults → 294 − 138 = 156<br><br>The difference between boys and adults is 156.<br>Check: adults 138 + girls 414 + boys 294 = 846. ✓