Question 1057406
Let s be the speed of the boat in still water. Then:
15/(s+8) + 15/(s-8)=2
15(s-8)+15(s+8)=2(s²-64)
2s²-30s-128=0
s²-15s-64=0
Using the quadratic formula,  {{{s = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}, we get two roots of 18.4658560997 and -3.46585609973. Throwing out the negative result, we get the speed of the boat in still water to be 18.47 kph. &#9786;&#9786;&#9786;&#9786;