```go
package main

import "fmt"

func main() {
	var t int
	fmt.Scan(&t)
	for i := 0; i < t; i++ {
		var a, b int64
		fmt.Scan(&a, &b)
		rem := a % b
		if rem == 0 {
			fmt.Println(0)
		} else {
			fmt.Println(b - rem)
		}
	}
}
```