Determine the Value of X to the nearest tenth of a centimetre.
I'll assume the fourth vertex is labelled C.
1. Find BC using the cosine rule: BC2 = 272 + 272 - 2*27*27*cos(70º)
2. Find x from the fact that sin(27º) = BC/x so that x = BC/sin(27º)
I'll leave you to crunch the numbers.