Answer :

AL2006

The area of any triangle = (1/2) x (length of the base) x (height)

2.5 centimeters  =  0.025 meter

The area of the sail is           (3.75) = (0.5) x (0.025) x (height)

Multiply each side by  2 :      (7.5) =            (0.025) x (height)

Divide each side by  0.025 :  (7.5)/(0.025) = height  =  300 meters

The situation is stupid, but the math is bullet-proof.