You need to find, first, the horizontal component of the inclined force (call it Wx), using an angle of 15 degrees (which is the angle between the inclined plane and the horizontal).
=> cos(15°) = Wx / 2.5 lb => Wx = 2.5 lb * cos(15°).
Second, you can find the inclined force , W, needed to produce the horizontal component Wx.
cos(33°) = Wx / W => W = Wx / cos (33°) = 2.5 lb*cos(15°) / cos(33°) = 2.88 lb
Answer: 2.88 lb
