Answer:
d = 4 + 6h
Explanation:
Given that :
Travel charge = $4 flat fee
Hourly charge = $6 per hour
Amount of dollar student can earn in an evening = d
Amount of hours spent babysitting = h
d = travel charge + (hourly charge * amount of hours) 
d = $4 + ($6 * h) 
d = 4 + 6h