The roots of the quadratic equation $\ldots \ldots \ldots \ldots$ are $-4$ and $5$.

Solve the following equation by using the quadratic formula,if the equation has a solution in $R$: $x^{2}-3x-4=0$.

The speed of a motorboat in still water is $9\,km/h$. In a river,it covers $12\,km$ downstream and the same distance upstream in a total time of $3\,hours$. Find the speed of the current of the river. (The speed of the current of the river is less than the speed of the motorboat in still water.) (in $,km/h$)

Solve the following equation using the method of factorization and write its solution set: $\frac{x+1}{x-1} + \frac{x-2}{x+2} = 3$

If the following quadratic equation has two equal and real roots,then find the value of $k$: $x(4 - kx) = 3 - 2x$.

Obtain the roots of the following equation using the method of 'completing the square': $m^{2} - 18m + 81 = 0$