Question

if 21is added four times to a number the result is 57 the number is

Answer 1

let the number be x
according to the question
21+21+21+21+x=57
x+84=57
x=57-84
x=-27

hope it helps you

Answer 2

21 + 4x = 57
4x =57-21
x=36/4
x=9