640 B | 640 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from datetime import datetime, timedelta
sys.setrecursionlimit(10**7)
BLANK = " "
#inp = input
inp = lambda : sys.stdin.readline().rstrip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
n = ii()
s = inp()
key = (ord(s[0]) - 97) - (ord(inp()) - 97)
ret = ""
for i in s:
ret += chr((ord(i) - 97 - key + 26) % 26 + 97)
p(ret)
if __name__ == "__main__":
tc = ii()
for t in range(1, tc+1):
ret = solve()