You need to set this up with a proportion and solve. 18/x-5 = 13.5/12.
cross multiply 13.5x-67.5=216
now solve for x
13.5x=283.5
x=21
the missing side is equal to 21-5, which is equal to16
Find the ratio of the two similar sides that both dimensions are given.
The smaller triangle aide that is 4 units is the similar side of the larger triangle given as 8 units.
8 / 4 =2, this means the larger triangle is 2 times the size of the smaller triangle, which also means the smaller triangle is 1/2 the size of the larger triangle.
X on the smaller triangle is 1/2 11 units which equals 5.5 units.
Y is 2 times 3, which equals 6 units.
x = 5.5
y = 6