That would be A...they have to have a constant ratio
R = speed in still water
r + c = speed with current
r - c = speed against current
3.5(r + c) = 70
r + c = 20
c = 20 - r
4(r + c) = distance from pier to pier
5(r - c) = distance from pier to pier
4(r + c) = 5(r - c)
4(r + 20 - r) = 5(r - 20 + r)
80 = 10r - 100
180 = 10r
18 = r
The speed in still water is 18 km/hour
Answer:
v = 220 yd²
Step-by-step explanation:
Small portion
v = 5 * 4 * 3
v = 60 yd²
Large portion
v = 9 * 6 * 3
v = 162 yd²
Total
v = 60 + 162
v = 220 yd²
