You can put this solution on YOUR website!
There seems to be a problem with this question.
The base of the pyramid is given as an isosceles triangle. Two long sides (equal) and a third, shorter, side.
The dihedral angle is the (smallest) angle between the sloping face of the pyramid and one of the base sides.
But, the dihedral angles are only all equal if the base is a regular shape, an equilateral triangle, square, regular pentagon, hexagon, etc. The body of the pyramid should also be regular. Not sloping.
Your two equal long sides will have the same dihedral angle but that will be different from the other one.
Does the dihedral angle apply to only the two equal sides ?
If so, then the problem is easily solved.
In any case the volume of a pyrimid is 1/3 times the area of the base times the vertical height (from the base to the height of the apex).