import sys
from typing import List

def main(_: int, m: int, l: List[int], r: List[int]):
    if not (sum(l) <= m <= sum(r)):
        return -1
    
    if m == sum(l):
        return (m * m - sum(e * e for e in l)) // 2
    
    def clamp(v: int, l: int, r: int):
        return max(l, min(v, r))
    
    def get_sum(t: int):
        return sum(clamp(t, a, b) for a, b in zip(l, r))
    
    tl, tr = 0, 10 ** 9 + 10
    while abs(tr - tl) > 1:
        t = (tl + tr) // 2
        if get_sum(t) < m:
            tl = t
        else:
            tr = t

    t0, d = tl, m - get_sum(tl)
    x = 0
    for a, b in zip(l, r):
        c = clamp(t0, a, b)
        if d > 0 and a <= t0 < b:
            c += 1
            d -= 1
        x += c * c
    
    return (m * m - x) // 2

if __name__ == '__main__':
    t = int(sys.stdin.readline().rstrip())
    answers = []
    for _ in range(t):
        n, m = map(int, sys.stdin.readline().rstrip())
        l = list(map(int, sys.stdin.readline().rstrip()))
        r = list(map(int, sys.stdin.readline().rstrip()))
        answers.append(main(n, m, l, r))
    print('\n'.join(map(str, answers)))