```go
package main

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

const mod int64 = 1000000007

type FastScanner struct {
	r *bufio.Reader
}

func NewFastScanner() *FastScanner {
	return &FastScanner{r: bufio.NewReaderSize(os.Stdin, 1<<20)}
}

func (fs *FastScanner) NextInt() int {
	sign, val := 1, 0
	c, err := fs.r.ReadByte()
	for (c < '0' || c > '9') && c != '-' {
		c, err = fs.r.ReadByte()
		if err != nil {
			return 0
		}
	}
	if c == '-' {
		sign = -1
		c, _ = fs.r.ReadByte()
	}
	for c >= '0' && c <= '9' {
		val = val*10 + int(c-'0')
		c, err = fs.r.ReadByte()
		if err != nil {
			break
		}
	}
	if err == nil {
		_ = fs.r.UnreadByte()
	}
	return sign * val
}

func powmod(a, e int64) int64 {
	res := int64(1)
	for e > 0 {
		if e&1 == 1 {
			res = res * a % mod
		}
		a = a * a % mod
		e >>= 1
	}
	return res
}

func isLucky(x int) bool {
	for x > 0 {
		d := x % 10
		if d != 4 && d != 7 {
			return false
		}
		x /= 10
	}
	return true
}

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

	n := in.NextInt()
	k := in.NextInt()

	cnt := make(map[int]int)
	unlucky := 0

	for i := 0; i < n; i++ {
		x := in.NextInt()
		if isLucky(x) {
			cnt[x]++
		} else {
			unlucky++
		}
	}

	fact := make([]int64, n+1)
	invFact := make([]int64, n+1)
	fact[0] = 1
	for i := 1; i <= n; i++ {
		fact[i] = fact[i-1] * int64(i) % mod
	}
	invFact[n] = powmod(fact[n], mod-2)
	for i := n; i >= 1; i-- {
		invFact[i-1] = invFact[i] * int64(i) % mod
	}

	comb := func(nn, rr int) int64 {
		if rr < 0 || rr > nn {
			return 0
		}
		return fact[nn] * invFact[rr] % mod * invFact[nn-rr] % mod
	}

	m := len(cnt)
	lim := k
	if m < lim {
		lim = m
	}

	dp := make([]int64, lim+1)
	dp[0] = 1
	processed := 0

	for _, c := range cnt {
		up := processed
		if up > lim-1 {
			up = lim - 1
		}
		for j := up; j >= 0; j-- {
			dp[j+1] = (dp[j+1] + dp[j]*int64(c)) % mod
		}
		processed++
	}

	ans := int64(0)
	for j := 0; j <= lim; j++ {
		ans += dp[j] * comb(unlucky, k-j) % mod
		if ans >= mod {
			ans -= mod
		}
	}

	fmt.Fprintln(out, ans%mod)
}
```