The crossing point of the two lines= centre point of the rectangle.
This centre point is also the bottom of the perpendicular height of 4m given.
Draw a line from the corner of the rectangle to the centre of the rectangle.
So: In the horizontal right triangle= adjacent side=1.5m and opposite.side=2.4m
With Pythagoras:
hypotenuse2=1.52+2.42
hypotenuse = √1.52+2.42
Hypotenuse ∴=√8.01
hypotenuse ∴=2.83malso adjacent side of vertical right angle triangle with Opposite side given=4m
So: In the vertical right triangle the hypotenuse = slope of pyramid
∴Slope2=2.832+42
∴Slope2=24.00892
∴slope=√24.0089
∴4.9m slope of the pyramid.