Me with this uwhat is the benefit of  modeling  real-world phenomena with mathematical expressions?

The modeling with mathematical expressions allow to make predictions about the thing being modeled. For example, we can predict if the population of the country will decrease or increase. What velocity has to have the spaceship to get to the other planet. How long it takes travel from on city to another by plane and by car. How many schools should be build during next 10 years. 

Step-by-step explanation:

19. 18-4.62=13.38 to spend on the systems or 6.69 a piece

20. 45000+300m=60000

m=50

45000+300m>60000  

He needs at least 50 machines to make the 60000.