Answer:
[tex]5.4x+15[/tex] inches
Step-by-step explanation:
This is an equilateral triangle.
Therefore, all sides are equal to each other. This means that we don't need to go through the whole hassle of adding up all the sides together. We can just take the easiest side and multiply it by 3 (as the perimeter of an equilateral triangle is [tex]3s[/tex], s being the side length.)
In my opinion, the side [tex]1.8x+5[/tex] is the easiest to work with.
Let's multiply this by 3.
[tex]3(1.8x+5)[/tex]
We can apply the distributive property - multiply all terms inside the parentheses by 3.
[tex]1.8\cdot 3 = 5.4\\5\cdot3 = 15\\\\5.4x+15[/tex]
Hope this helped!
