1. sin(theta) = -0.4545 = - 4545/10000 = - 909/2000 (reduce it to lowest terms)
You have to first express it in terms of a fraction.
sin(theta) = y/r
So you got y and you got r. Since theta is in 4th quadrant, x is positive and y is negative. Use the Pythagorean theorem to find x and choose the positive root, then replace in cos(theta) = x/r
x^2 + y^2 = r^2
2. Sec is the reciprocal for cos. So if cos(theta) = x/r, then sec(theta) = r/x. You know how to continue.