Answer:
It depends, but probably 63.5902 or 63.59
Explanation:
If you mean adding 53.89 + 18% of 53.89 then...
18% = .18
53.89 x .18 = 9.7002
53.89 + 9.7002 =
63.5902
if rounded, it's 63.59
If you mean that adding the actual 18% as a decimal with 53.89 then...
18% = .18
53.89 + .18 =
54.07