$0.75D ; 10s miles
Step-by-step explanation:
1)
Given that:
List price of phone = $D
Advertised price = 25% off the list price
Hence, sales price of phone :
(100% - 25%) × list price
Sales price = 75% × $D
Sales price = $0.75D
2)
Given that :
Time of travel = 10 hours
Speed of travel = s miles per hour
Total distance traveled = (speed of travel × time of travel)
Total distance traveled = (10 * s) miles