30分研究一下午了求指导

#include<iostream>
using namespace std;
int main()
{
	int s, v, t;
	cin >> s >> v;
	if (s % v == 0)
	{
		t = s / v;
	}
	else
	{
		t = s / v + 1;
	}
	t += 10;
	int t1;
	int a, b;
	if (t <= 480) {
		t1 = 480 - t;//出发的时间
		a = t1 / 60;//出发的时
		b = t1 % 60;//出发的分
		if (!(b < 10)) {
			cout << a << ":" << b << endl;
		}
		else {
			cout << a << ":0" << b << endl;
		}
	}
	else if (t > 480) {
		t1 = 1920 - t;//出发的时间
		a = t1 / 60;//出发的时
		b = t1 % 60;//出发的分
		if (a >= 10) {
			if (b >= 10) {
				cout << a << ":" << b << endl;
			}
			else {
				cout << a << ":0" << b << endl;
			}
		}
		else {
			if (b >= 10) {
				cout << "0" << a << ":" << b << endl;
			}
			else {
				cout << "0" << a << ":0" << b << endl;
			}
		}
	}
	return 0;
}