It's the "tell whether the number is rational or irrational" section that i'm struggling with

The ratio of men to women working for a company is 4 to 5 . if there are 90 women working for the company, what is the total number of employees?

Two cyclists 84 miles apart start riding toward each other at the same. one cycles 2 times as fast as the other. if they meet 4 hours later, what is the speed (in mi/h) of the faster cyclist?

Acompany that manufactures and sells guitars made changes in their product range. from the start they had 20 models. then they reduced the number of models to 15. as a result, the company enjoyed a 10% increase in turnover. - how much did the stock level change? in (%)