, 2023

In 1 hour, Liang paints $\frac{1}{3}$ of the room.

Thus, in 2 hours, Liang paints $\frac{2}{3}$ of the room.

Edmundo needs to paint $1 - \frac{2}{3} = \frac{1}{3}$ of the room.

In 1 hour, Edmundo paints $\frac{1}{4}$ of the room.

Since $\frac{1}{4} = \frac{3}{12}$
and $\frac{1}{3} = \frac{4}{12}$,
this means that Edmundo paints for $\frac{1}{3} \div \frac{1}{4} = \frac{4}{12} \div \frac{3}{12} = \frac{4}{3}$ of an hour.

Therefore, Edmundo paints for 80 minutes.
When converted to a fraction, $A\%$ is equal to $\dfrac{A}{100}$.

When an amount is increased by $A\%$, we can find its new value by
multiplying by $1 + \dfrac{A}{100}$.

When an amount is decreased by $A\%$, we can find its new value by
multiplying by $1 - \dfrac{A}{100}$.

When $400 is increased by $A\%$,
the amount becomes $\$400\left(1 + \dfrac{A}{100}\right)$.

When this value is decreased by $A\%$, the amount becomes $\$400\left(1 + \dfrac{A}{100}\right)\left(1 - \dfrac{A}{100}\right)$.

Therefore, $$\text{400 (1 + A 100 ) (1 - A 100 ) amp; = 391 (1 + A 100 ) (1 - A 100 ) amp; = 391 400 1 - A 2 100 2 amp; = 1 - 9 400 A 2 100 2 amp; = 9 400 A 2 100 2 amp; = 3 2 20 2 A 100 amp; = 3 20 (since A gt; 0 ) A amp; = 100 3 20 = 15}$$ Therefore,
$A = 15$.