Question 828815
That's an odd value.  
.
H * W = 40.5
Since they are equal,
H^2 = 40.5
Take the square root of each:
H = 6.364
(and therefore W = 6.364)
.
If the value is something else, simply take its square root.
OR, possibly...
Is the sail triangular rather than square?  If so, then solve it this way:
h^2 = 1/2 40.5
h^2 = 20.25
h = 4.5 feet
That makes a lot more sense.  This question really should be clarified as there are different sorts of "sails" and rarely would one be a triangle yet have the same base and height.  *sigh*