3-4

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