Find the magnitude of the magnetic flux through the floor of a house that measures 21m by 13m . Assume that the Earth's magnetic field at the location of the house has a horizontal component of 2.4×10−5 T pointing north, and a downward vertical component of 4.3×10−5 T .

I can't seem to get the correct answer so i think I might be going about the problem the wrong way.

This is what I did.

Bx= 2.4x10-5 T
By= 4.3x10-5 T
Bnet= (Bx^2 + By^2)^.5 = 4.9x10-5 T
angle= tan^-1(By/Bx)= 60.83

A= 21m x 13m= 273m^2
Magnetic flux= Bcos angle A
magnetic flux= .00651 Wb

My answer was incorrect, any ideas what the right way to approach this problem is??