Answer:
a=m/f is not an equation under newton's second law
Explanation:
newton's second law of motion is represented using: f=ma
where a=v-u/t
therefore it becomes,f=m(v-u)/t
from f=ma,
a will become f/m,
m will become f/a
If the current takes him downstream we must find the resultant vector of the velocities:

Then if the river is 3000 m-wide the swimmer will have to pass:
1.3520747 · 300 = 4056.14 m t = 4056.14 m : 1 m/s
a ) It takes
4056.15 seconds ( 1 hour 7 minutes and 36 seconds ) to cross the river.
b ) 0.91 · 3000 =
2730 mHe will be 2730 m downstream.