How to do word problems where two quantities are unknown Practice Test

Michael has red shirts and blue shirts, such that the ratio is red shirts for every blue shirts. What is the minimum number of shirts he can have?

A helicopter flies against the wind from city A to city B in 5 hours. The same helicopter returns from city B to city A, in the same direction as the wind, in 4 hours. Find the ratio of the speed of the helicopter to the speed of the wind.