a$)$ Solve the differential equation.

$y^{\text{'}}=\frac{6x^{5}y}{lny}$

b$)$ Find the solution of the differential equation that satisfies the initial condition $y(0)=6.$

$\frac{dy}{dx}=8x^{7}y$

c$)$ A tank contains $200$ L of brine with $12$ kg of dissolved salt. Pure water enters the tank at a rate of $6\frac{L}{m}in.$ The solution is kept thoroughly mixed and drains from the tank at the same rate. How much salt is in the tank after $20$ minutes?