package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
)

func main() {
	in := bufio.NewReaderSize(os.Stdin, 1<<20)
	out := bufio.NewWriterSize(os.Stdout, 1<<20)
	defer out.Flush()

	var t int
	fmt.Fscan(in, &t)
	for ; t > 0; t-- {
		var n, k int
		fmt.Fscan(in, &n, &k)

		a := make([]int, n)
		b := make([]int, n)

		for i := 0; i < n; i++ {
			fmt.Fscan(in, &a[i])
		}
		for i := 0; i < n; i++ {
			fmt.Fscan(in, &b[i])
		}

		sort.Ints(a)
		sort.Slice(b, func(i, j int) bool {
			return b[i] > b[j]
		})

		for i := 0; i < k && i < n; i++ {
			if b[i] > a[i] {
				a[i] = b[i]
			} else {
				break
			}
		}

		sum := 0
		for _, v := range a {
			sum += v
		}
		fmt.Fprintln(out, sum)
	}
}