Question 266590
This is a RTD problem. Here is a table based on given information
paddle . . . . . . . . .rate . . . . . . . . . time . . . . . . . . . distance
up stream . . . . . .r - c . . . . . . . . . . .10 . . . . . . . . . . 10r - 10c =15
down stream . . . .r + c . . . . . . . . . . .5 . . . . . . . . . . .5r + 5c = 22.5
totals . . . . . . . . . 
Looking at column 3 we get
(i) 10r - 10c = 15
(ii) 5r + 5c = 22.5
multiply (ii) by 2 to get
(iii) 10r + 10c = 45
add (i) and (iii) to get
(iv) 15r = 60
divide to get
(v) r = 4
This means that the current is
c = 2.5