The length of side KL is 13 centimeters. Among the provided answer choices, the correct option is 13 cm.
How to find the length of side KL
To find the length of side KL, add up the lengths of all four sides of the quadrilateral and set it equal to the given perimeter of 90 centimeters:
JK + JL + LM + KL = 90
Substitute the given expressions for the lengths of the sides:
(n + 7) + (3n + 4) + (2n - 12) + n = 90
Combine like terms:
7n - 1 = 90
Add 1 to both sides:
7n = 91
Divide both sides by 7:
n = 13
Now that we have the value of n, substitute it into the expression for side KL:
KL = n = 13 cm
Therefore, the length of side KL is 13 centimeters. Among the provided answer choices, the correct option is 13 cm.