Programming Challenge: a classic trigonometry problem

[Gil]

Just tried today to tackle the problem.

Just wrote the equations of the red line and green line.

Had them cross at y=15

From there, I could eliminate the intercept of green equation.

And used the solver of the HP50G for the found Polynomial expression.

But I get two real values (solutions ?):
15.98 and 28.3565769436.