let's say the number is x
5 times a number is 5 times x or 5x
5 times a number less than 18 means 18 decreased by 18 times a number or 18-5x
equals 13
18-5x=13
minus 18 both sides
-5x=-5
divide both sides by -5
x=1
the number is 1
the phrase is 18-5x=13 where the number is x