Find the transformation matrix that rotates the axis x3 of a rectangular coordinate system 45 degree towards x1 around x2 axis ( i understand how to find the matrix what i'm confuse is the rotation around the x2 axis) explain in detail.

Suppose that a cylindrical tank 6 meters high with a radius of 2 meters is filled to the rim with water. the tank is buried so that the top of the tank is 1 meter below ground level. the space above the tank is not filled with water. calculate how much work needs to be done by a pump to pump the water out of the tank up to ground level. (the water weighs 9,800 newtons per cubic meter.)