18. sides are all same length so 5-2x=-4x+9 solve add 4x both sides 5+2x=9 mins 5 both sides 2x=4 x=2
sub back 5-2x=5-2(2)=5-4=1 the length of each side is 1 3 sides so the perimiter is 3 units
19. same side length so 3(x-1)=5x-6 distribute 3x-3=5x-6 minus 3x both sides -3=2x-6 add 6 both sides 3=2x divide 2 3/2=x sub back 5x-6 5(3/2)-6 15/2-6 7.5-6 1.5
5 sides so 1.5 times 5=7.5 units is the perimiter which is about 15/2 units
20. we can't see what's after the x+? so this is a mystery quesiton
