If minivans and cars were sold at a 3:5 ratio each day and there were 12 minivans sold yesterday they would have sold 20 cars.
You can find this by dividing 12(the number of minivans sold) by 3(the ratio of vans v.s. cars), which equals 4. To find the amount of cars sold, use the same method, only multiply with by the ration of cars. 5*4 = 20