​A man rows at 5km/h in still water. If the river is running at 1km/h, it takes him 75 minutes to row to a place and back. How for is the place?​

Correct option is C

Given:

​A man rows at 5km/h in still water. If the river is running at 1km/h, it takes him 75 minutes to row to a place and back.

Formula used:

​$$\mathrm{\frac{D}{V+U} + \frac{D}{V-U} = T}$$

where, 

V = Speed of the boat in still water
U = Speed of the current or river

T = Time

Solution:

V = 5km/h​

U = 1km/h

T = 75 minutes = 1.25 h

$$\mathrm{\frac{D}{V+U} + \frac{D}{V-U} = T}$$

$$\mathrm{\frac{D}{5+1} + \frac{D}{5-1} = 1.25}$$

$$\mathrm{\frac{D}{6} + \frac{D}{4} = 1.25}$$

$$\mathrm{\frac{2D+3D}{12} = 1.25}$$

5D = 1.25 × 12

D = $$\frac{15}{5}$$

D = 3

The distance to the place is 3 kilometers.

Thus, the correct answer is (c).