The answer is C = 3
If we substitute 3 into the x values in each equation we can see that the top and bottom is the same value and both sides are also the same value, meaning that it is a parallelogram;
Top and bottom of parallelogram:
2x + 3
2 (3) + 3
= 6 + 3
= 9
And
x + 6
(3) + 6
= 9
And then the two sides;
6x - 5
6 (3) - 5
= 18 - 5
= 13
And
4x + 1
4 (3) + 1
= 12 + 1
= 13
There are two pairs of equal sides which shows that this is a parallelogram.
