n = int(input())

def time():
    x,t1,t2,sgn = [],0,0,0
    x = list(input())
    t1 = (int(x[0]+x[1])*3600
        +int(x[3]+x[4])*60
        +int(x[6]+x[7]))
    if len(x) == 17:
        t2 = (int(x[9]+x[10])*3600
              +int(x[12]+x[13])*60
              +int(x[15]+x[16]))
    else:
        if x[19] == '-':
            sgn = -1
        elif x[19] == '+':
            sgn = 1
        t2 = (int(x[9]+x[10])*3600
              +int(x[12]+x[13])*60
              +int(x[15]+x[16])+sgn*int(x[20])*24*3600)
    return abs(t2 - t1)

p1,p2,r_t = 0,0,0
for i in range(n):
    p1 = time()
    p2 = time()
    r_t = int((p1+p2)/2)
    print('{:02d}:{:02d}:{:02d}'.format(r_t//3600,r_t%3600//60,r_t%60))

线下示例运行没问题，但洛谷全是RE