10 yuan 12 Yes, 2 yuan is twice as much as 10 yuan, so 2 yuan should be 12*2=24, and 5 yuan is 51-24-12 =12.

9. If the number of small and medium-sized cards is X, then the number of large cards is 42-2x.

10 *(42-2x)+8x+5x = 3 15

420-7x=3 15

x= 15

So the number of large trucks is 12, and the number of medium trucks and small trucks is 15.