Whitney left school and drove 7 miles to meet her mother at a restaurant. her mother left at the same time and drove 8 miles, traveling 5 miles faster then her daughter. if the two arrived at the restaurant at the same time, what was whitney's speed

Let's write the cinematic equation for Whitney and her mother.
 We have then:
 For Whitney:
 d = v * t
 7 = v * t
 For her mother:
 d = (v + 5) * t
 8 = (v + 5) * t
 Where,
 v: speed
 t: time
 We have then how the time is the same:
 7 / v = 8 / (v + 5)
 We cleared v:
 7 (v + 5) = 8v
 7v + 35 = 8v
 8v-7v = 35
 v = 35 mph
 
 whitney's speed is:
 v = 35 mph

19095705.3333  is the answer
 
hope i helped!