Work and Energy--Combining equations Hi, I have the following sample problem that I am having difficulty combining equations: The power expended in lifting an 825-lb girder to the top of a building 100 ft. high is 10.0 hp. How much time is required to raise the girder. So the data is: F= 825 s= 100 ft P= 10.0 t= ? Now the following two equations contain all the values we need: P=W/t and W= Fs In the text the combined equations are shown as: t= W/P = Fs/P ----- How was this found and combined? Thanks.