David K. answered • 12/20/15

I will help you find what you're stuck on, I am patient

First line of action would be to find the missing angle P. All angles in a triangle add up to 180º so it is just a simple matter of subtracting the known angles from 180 to see what is left over

180 - 117 - 18 = 45

∠P = 45°

Here is where we would use what is called the sine rule. which is as follows for an ABC triangle

a/sin(A) = b/sin(B) = c/sin(C)

so on ΔPQR

p/sin(P) = q/sin(Q) = r/sin(R)

we can now assume

q/sin(Q) = p/sin(P)

45/sin(117) = p/sin(45)

now we just solve for our missing side p

p = (45/sin(117))/sin(45) or p = 45/(Sin(117)*sin(45))

p = 71.4 cm