Tracie drove for 17 hours.
Explanation:
Given that,
Tracie and Marcia drove to Northern California to see Marcia’s sister Eureka.
Let us assume,
- The number of hours drove by Marcia be 'x'.
- The number of hours drove by Tracie is one hour more than four times as much as Marcia.
⇒ one hour more than four times of Marcia = 1+4x
The trip took a total of 21 driving hours.
To find the number of hours Marcia drove :
⇒ Tracie hours + Marcia hours = Total hours.
⇒ (1+4x) + x = 21
⇒ 1 + 5x = 21
⇒ 5x = 20
⇒ x = 20/5
⇒ x = 4
Therefore, Marcia drove for 4 hours.
To find the number of hours Tracie drove :
Substitute x=4, in (1+4x)
⇒ 1+4(4)
⇒ 1+16
⇒ 17 hours.
∴ Tracie drove for 17 hours.