The question seems to be incomplete!
On your calculator, there should be a Tan button. Hit that, then type in 81. Voila! Tan81 = 6.313751515 (As far as my calculator shows.)
tan-1(0.575) = 29.8989 degrees (rounded)
Tangent is 0.5317
=(sqrt(3)*(3-sqrt(5))-sqrt(50-22*sqrt(5)))/2