Big oh notation run time

Question

I have this Question , I want the answer and show me how to solve it Please :

Analyze the running time of the following algorithm using Big-Oh notation

maxerea =0; maxpt1 =maxpt2 = maxpt3 =0;
for(i =1;i<=n;i++)
    for(j =i+1;j<=n;j++)
       for(k =j+1;k<=n;k++){
           empty = True;
         for(l =1;l<=n;l++){
         if((l != i) && (l != j) && (l != k))
            if insideTriangle(i,j,k,l) then empty = False;
            }
              area = TriangleArea(i,j,k);
            if (area < maxarea) {
                maxarea =area;
                  maxpt1 = i; maxpt2 = j; maxpt3 = k;
               }
           }
  print, maxpt1, maxpt2, maxpt3