3-4

#include<stdio.h>
int main(void)
{
    double x,y;

    printf("Enter x:");
    scanf("%Lf",&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;
}