Suppose the base of the triangle is x.
x×6÷2=18
Then you work out the equation
x×6=18×2
x×6=36
x=36÷6
x=6
That means the base is 6 inches
If you want to check, you just have to plug 6 into x
6x6÷2=36÷2
=18 inches
So that means 6 inches is definitely the answer
Hope this helps!