Hi Cynthia. I think you did a great job of this. 3600 is 60 x 60 (that factor converts the "per second" into "per hour"). I don't see an easier way to do this than you are already using.

You could write it in one algebraic expression. If R is the rate per second (R = 3 in your case), then the amount it can do in 15 hours is R x 3600 x 15. Then you express the result in scientific notation.

Keep it up Cynthia, you're doing fine!
Stephen La Rocque.