[求助]PREP数学题

At a certain bakery, each roll costs r cents and each doughnut costs d cents. If Alfredo brought rolls and doughnuts at the bakery, how many cents did he pay for each roll?

1)Alfredo paid $5.00 for 8 rolls and 6 doughnuts.

2)Alfredo would have paid $10.00 if he had bought 16 rolls and 12 doughnuts.

答案是E.

根据1，2两个条件列方程式，化简以后2的方程式与1同，故不能求出这个二元一次方程的解。选E