0.2 is the same as 2/10
18/(2/10)
As you may have learned in school, when you divide a fraction, you flip the fraction in the denominator, and change it to multiplication
18/(2/10) becomes 18 x (10/2)
multiply normally
18 x 10 = 180
divide to find answer
180/2 = 90
90 is your answer
hope this helps
Remember, when you meet this problem, flip the second fraction, and change the division sign into multiplication. (always second, never first (if first is a fraction)).