This is so much straight forward problem. So the source code is given below with out any explanation.

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<string.h>
 
int main ()
{
 
        int term1,term2,final,attendance,class_test[3],temp;
        int test,t,i,total,k,m;
        char grade[100][4];
        scanf("%d",&test);
        t=test;
        i=0;
        while(test)
        {
            scanf("%d %d %d %d ",&term1,&term2,&final,&attendance);
            scanf("%d %d %d",&class_test[0],&class_test[1],&class_test[2]);
            for(k=0;k<3;k++)
             {
                 for(m=k+1;m<3;m++)
                 {
                       if(class_test[k]>class_test[m])
                       {
                              temp=class_test[k];
                              class_test[k]=class_test[m];
                              class_test[m]=temp;
                       }
 
                  }
 
              }
 
         total=term1+term2+final+attendance+((class_test[2]+class_test[1])/2);
 
         if(total>=90)
           strcpy(grade[i],"A");
         else if(total>=80 && total<90)
           strcpy(grade[i],"B");
         else if(total>=70 && total<80)
           strcpy(grade[i],"C");
         else if(total>=60 && total<70)
           strcpy(grade[i],"D");
         else if(total<60)
           strcpy(grade[i],"F");
           i++;
           test--;
     }
     for(i=0;i<t;i++)
      {
          printf("Case %d: %s\n",i+1,grade[i]);
      }
 
  return 0;
}