import math
import statistics

T = int(input())


time = [0 for i in range(3)]
for i in range(2*T+1):
    if i%2 == 0:
        if i==0:
            pass
        else:
            print("%02d:%02d:%02d"%(time[0]/2,time[1]/2,time[2]/2))
            time = [0 for i in range(3)]
    if i == 2*T:
        break
    a = list(input().split())
    a[0] = list(map(int,a[0].split(":")))
    a[1] = list(map(int,a[1].split(":")))
    if len(a) == 3:
        if int(a[2][-2]) == 1:
            a[1][0] += 24
        elif int(a[2][-2]) == 2:
            a[1][0] += 48
    if a[1][2] < a[0][2]:
        a[1][2] += 60
        a[1][1] -= 1
    elif a[1][1] < a[0][1]:
        a[1][1] += 60
        a[1][0] -= 1
    time[0] += a[1][0] - a[0][0]
    time[1] += a[1][1] - a[0][1]
    time[2] += a[1][2] - a[0][2]