How do i factor out the coefficient of variables?

Here is their argument. given the obtuse angle x, we make a quadrilateral abcd with ∠dab = x, and ∠abc = 90◦, and ad = bc. say the perpendicular bisector to dc meets the perpendicular bisector to ab at p. then pa = pb and pc = pd. so the triangles pad and pbc have equal sides and are congruent. thus ∠pad = ∠pbc. but pab is isosceles, hence ∠pab = ∠pba. subtracting, gives x = ∠pad−∠pab = ∠pbc −∠pba = 90◦. this is a preposterous conclusion – just where is the mistake in the "proof" and why does the argument break down there?

Apair of ordinary dice is rolled. what is the probability that each die will show a number higher than 4. 1. (1/36) 2. (1/12) 3. (1/6) 4. (1/4) 5. (1/3)

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)