Hey there!!
Let us take the number as ' x '
20% of x
= (20/100) × ( x )
= ( 1/5 ) × ( x )
= x/5
The number is decreased by 20% of itself
x - x/5 = 56
5x - x / 5 = 56
4x/5 = 56
Multiplying by 5 on both sides
5x = 56 × 5
5x = 280
dividing by 5 on both sides
4x / 4 = 280 / 4
x = 70
The number is 70
Hope my answer helps!