Any rhombus has the same length for all for sides, so:
x + 14 = 3x +4
So, we get x = 5
Now, we can write
x + 14 = 8y
Since x = 5,
19 = 8y
so y = 19/8 = 2.375
You can take any one of the equations and substitute the value of x or y in. The length is 19