Answer:
Let's take a look at the lengths of the sides: 90, 120, 150. What do we notice here?
It's a 3:4:5 triangle.
90/30 = 3, 120/30 = 4, 150/30 = 5.
That the 2 triangles formed by line running diagonally through the base creates AT LEAST 2 right angles.
Since the total amount of degrees in a quadliateral is 360,
180(s-2)
And we know that there are 2 right angles which equals to 180 and the sides are all parallel to each other,
That must mean that the 2 remaining angles of the box add up to 180,
Therefore all angles are 90 degrees.