If a 370 M sample of A is heated to 500 K what is the concen

If a 3.70 M sample of A is heated to 500 K, what is the concentration of B at equilibrium?

At equilibrium let the concentraion of A become

3.7 - x

so that of B formed will be 2x

hence

4x^2 / (3.7 - x) = 7.08 * 10^-6

Solve to get the value of x

x = 2.56 * 10^-3

Hence the equilibrium concentration of B = 2x = 5.11 * 10^-3 M