Answer: A, line JK is 4 units long.
Explanation:
Considering all side lengths of a parallelogram are the same, you are looking for an equation that would allow you to equate both sides to each other, like how X is equal to 5, since 20 / 5 = 4, hence 4x being 20 since it's 4 times 5.
For this to work with Y, 2y would be equal to 8, and eight minus one of course equals 7. y + 3 is also equal to 7.
This means you just substitute 4 in for Y to get 8 - 1 and 4 + 3. :)