Please help me with this graph derivative problem?

Question

http://s141.photobucket.com/albums/r77/rocketllamafootie/?action=view¤t=combines.jpg

Answer 1

Use the lower graph do determine x and the slope dx/dt at t = 15hrs. Get the value of x directly from the curve, and the slope by drawing a line tangent to the curve at t = 15, and measure the slope of that tangent line.

Using the value of x from above, go to the upper curve and get the value of ds/dx for that value of x.

The velocity is ds/dt, and ds/dt = dx/dt * ds/dx. You have both dx/dt and ds/dx from the graphical measurements.