#5
Parallelograms require that opposite sides be congruent.
Therefore we can form a system of linear equations by equating the lengths of opposite sides.
For top and bottom sides, we have
4x+y=8 .............(1)
For left and right sides, we have
2x+y=6..............(2)
Subtract (2) from 1
4x+y-(2x+y)=8-6 =>
2x=2 =>
x=1
Substitute x=1 in (1)
4(1)+y = 8
y=4
Answer: x=1,y=4
Check: top side = 4(1)+4=8, ok.
left side = 2(1)+4=6, ok.