Answer:
Speed of river's current = 5 mph
Step-by-step explanation:
Let 'd' be the distance covered
Let x be the speed of the rivers current
Speed upstream = 15-x
speed downstream = 15+x
Time = distance / speed
time upstream = 
time downstream = 
the ferry trip upstream takes twice as long as its return trip downstream
= 
divide both sides by d
= 
cross multiply


Add 2x on both sideds

subtract 15 from both sides and divide by 3

x=5
Speed of river's current = 5 mph
Mikayla subtracted 4 from both sides in the beginning when she should've added it to both sides to cancel it out on the right. the correct answer should actually be x=1
The answer is 29. Hope this helps.
From the given problem above, the correct answer would be the last option since it stated that a number which is X is increased by five or added by five and then the sum is then squared. Therefore, it is option D. (X+5)^2.