There are three drains in a 6-meter-deep reservoir of water. To lower the water level by 2 meters it takes drain A 2 hours, drain B 3 hours, and drain C 4 hours. If all three drains are opened at once, how long will it take to empty the reservoir?

Mental Meaths \( 1,12 x=84 \) \( 2,20 x=20,300 \) \( 3,60 x=1800 \) \( 4,4 x=300 \) \( 5,31 x=93 \)

3. ¿Cuál es la longitud de onda de la radiación ultravioleta del hidrógeno correspondiente a la transición de \( n_{i}=2 \) a \( n_{f}=1 \) ?

4. Show that \( \left|\begin{array}{lll}a & b & c \\ a^{2} & b^{2} & c^{2} \\ b+c & c+a & a+b\end{array}\right|=k(a+b+c)(b-c)(c-a)(a-b) \) and tence determne the value of \( k \)

Factor. \[ 64-49 y^{2} \]

List the factors of 60 . Is this number prime or composite?