1. The resultant force is equivalent to the hypotenuse of the triangle formed by the component forces, and the angle between the result and each component is found with trig based on that premise. You're looking for the angle formed by the hypotenuse and the longer of the two sides, so the larger component is used as the adjacent side and the smaller as the opposite side. So the angle is given by the inverse tangent of 7/14, or equivalently of 1/2.
A suitable calculator can tell you the loan payment will be $526.23 monthly. The same calculator can also tell you the total of 60 payments exceeds the loan amount by $3073.80.
