#include <stdio.h>int main() {double x, y;scanf("%lf", &x);if (x <= 15) {y = 4 * x / 3.0;} else {y = 2.5 * x - 10.5;}// printf("f(%.2f)=%.2f\n", x, y);printf("%.2f\n", y);return 0;}  完善：