8a-25b-5 is the answer to ur question
9, 2, -5... so is going down by 7 each time, meaning the "common difference" is -7.
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
Initial velocity (u) = 0m/s
Final velocity (v) = 20m/s
Time (t) = 10 s
Acceleration (a)
= (v - u)/t
= [(20m/s) - (0m/s)]/10s
= (20m/s)/10s
= (20m/s²)/10
=> 2m/s²