If Ann can build the model in 3 hours, then in 1 hour she gets 1/3 of it done. Likewise, if Sam can build the model in 6 hours, then in 1 hour he gets 1/6 of it done. We are looking to find how long it takes when they combine their efforts, so we will add the two together and set it equal to 1/x, x being the number of hours it takes for both of them to get the whole job done. The equation then looks like this: [tex] \frac{1}{3}+\frac{1}{6}=\frac{1}{x} [/tex]. You will have to find the common denominator to add those fractions, and once you do, cross multiply to solve for x.
