Answer
20 and 21
Work Step by Step
Note, the 5 step process is as follows:
(1) Familiarize yourself with the problem.
(2) Translate the problem into Algebra.
(3) Solve.
(4) Check. Note, if we want to check a solution, we would plug it back into the equation and check that the equation yields a true statement.
(5) State the answer.
After becoming familiar with the problem, we find:
$$x\left(x+1\right)=420 \\ x^2+x-420=0 \\ x_{1,\:2}=\frac{-1\pm \sqrt{1^2-4\cdot \:1\left(-420\right)}}{2\cdot \:1} \\ x=20,\:x=-21$$
The page numbers are 20 and 21.