2-4

2#include<stdio.h>
int main(void)
{
   double x,y;                       
   printf("Enter x(x>=0)：\n"
    scanf("%lf,&x");
      if(x<=15){
       y=4*x/3;
    }
    else{
        y=2.5*x-10.5;
    }
    printf("y=f(%f)=%.2f\n",x,y);

   return 0;
}