Question 763338
Trip to water park averaged 36mph
= D/36
Trip from water park averaged 80mph
= D/80
So, D/36 + D/80 = 2.9
Common denominator = 2880
   (80D + 36D)/2880  = 2.9
Cross multiply
116D = 2880 * 2.9
116D = 8352
   D = 8352/116
   D = 72 miles
Distance one way to water park = 72 miles.
Proof:
D/36 + D/80 = 2.9
72/36 + 72/80 = 2.9
          2.9 = 2.9
Hope this helps.
:-)