First, lets draw a figure.

There are 3 variables: speed of boat 1, speed of boat 2, and width of the river.

Looks like we can write 2 equations. Given this, we cannot find all 3 variables - since we dont have 3 equations.

If we can reduce to 2 variables, we can solve for the 2 variables. Lets keep this in mind as we write down the equations.

Equation 1: Boat 1 covers a distance of (d - 140) while boat 2 covers a distance of 140. The time taken by both the boats is the same. This gives us the first equation.

\frac{d-140}{s_1}=\frac{140}{s_2}

Equation 2: Before the boats meet again, boat 1 covers 140 + (d - 60); and

boat 2 covers (d - 140) + 60

\frac{140\ +\ \left(d-60\right)}{s_1}=\frac{\left(d-140\right)\ +\ 60}{s_2}

That's it. We have 2 equations in 3 variables. We cannot solve for all 3. But, can we find d?

How about multiplying both equations by s1? We get

d-140=140\cdot\frac{s_1}{s_2} and

140+\left(d-60\right)=\left(\left(d-140\right)+60\right)\cdot\frac{s_1}{s_2}

Replacing s1/s2 with r (relative speed) gives us 2 equations in 2 variables. Now, we can solve for d and r.

We can figure out the width of the river; and the relative speeds of the boats. But, we cannot figure out the actual speed of the individual boats.