C++ :

#include <stdio.h>

int main()
{
  int casc;
  scanf("%d", &casc);
  for (int casi = 1; casi <= casc; casi++) {
    int v, t, t0, l;
    scanf("%d %d %d %d", &v, &t, &t0, &l);
    int s = v * t;
    double res = l / s * (t + t0);
    if (l % s == 0)
      res -= t0;
    else res += 1.0 * (l % s) / v;
    printf("%.3f\n", res);
  }
  return 0;
}