1800 (x+20)

Yes, they are all equivalent.

To prove, assume a real value of x, for instance, x = 2. Then we substitute this value to each expression. The answers must be equal since the expressions are equivalent:
1800(x+20) ; x=2
1800(2+20) = 1800(22) = 39,600

1800x + 20(1800) ; x=2
1800(2) + 36000 = 3,600 + 36,000 = 39,600

1800x + 36,000 ; x=2
1800(2) + 36,000 = 3,600 + 36,000 = 39,600

Hope this helps :)