3 x 2 is 6. 6 x 5 is 30.. There you go, the answer is 30.
The given expression, 81a^6 - 100, is a difference of two squares. The first term 81a^6 is a square of 9a³. The second term, 100, is a square of 10. The factors of the given expression is therefore, (9a³ - 10) x (9a³ + 10).
Points of inflections are zeroes of the second derivative. We have:

So, the second derivative equals zero if and only if

So, this is the only point of inflection of this function.
The first step is to rewrite the equations given in the problem.
y = 2x - 2 → 2x - y = 2
y = 2x + 2 → 2x - y = -2
y = 2 - x → x + y = 2
y = 4 - x → x + y = 4
Then let u = 2x - y and v = x + y. Therefore we get the equations with the following bounds -2 ≤ u ≤ 2 and 2 ≤ v ≤ 4.