What is the length of a side of the pentagon?

The length of a side of a pentagon is 69 units.

Since the hexagon on the left has 6 sides, and all of the sides have an equal length, if you multiply the number of sides(6) by the length of one side (3x+5) you will get the perimeter of the hexagon, 6(3x+5)
This is the same for the pentagon as well, since the pentagon on the right has 5 sides, and all of the sides have an equal length, if you multiply the number of sides(5) by the length of one side (4x-1) you will get the perimeter of the pentagon, 5(4x-1)

Now we have the equation for the perimeter of the hexagon, 6(3x+5), and the pentagon 5(4x-1). Since we know that the perimeters are the same length for each shape, we can set these two formulas equal to each other

Here is how I set up my equation
6(3x+5)=5(4x-1)

Now that you have the equation, you must solve for x, which I will demonstrate the steps down below

6(3x+5)=5(4x-1)
18x+30=20x-5 (subtract 18x on both sides)
30=2x-5 (subtract -5 on both sides)
35=2x (divide 2 on each side)
17.5=x

Now that you have determined that x is 17.5, all that is left to do is plug in 17.5 into the equation that solves for one side of the pentagon(4x-1) to get the length of a side of a pentagon, which is your answer.

Here is the work if needed
4(17.5)-1
70-1
69

The length of a side of a pentagon is 69 units.

I hope this helped!
Leave a comment on my answer if you have any questions on what I said here or need any more help with math.

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.