Three times the teacher’s pay equals seven times the driver’s, so Teacher : Driver = 7 : 3. The 4-unit gap is the $2100 the teacher earns more.<br><br>[[model:questions/solutions/q4199.png]]<br><br>• 3 × Teacher = 7 × Driver ⇒ Teacher : Driver = 7 : 3<br>• Difference → 7 units − 3 units = 4 units → $2100<br>• 1 unit → $2100 ÷ 4 = $525<br>• Driver → 3 units = 3 × $525 = $1575<br><br>The bus driver’s monthly salary is $1575.<br>Check: Teacher 7 × $525 = $3675; 3 × $3675 = $11025 = 7 × $1575. ✓