Combining Equilibrium Constants

By the end of this video, you should understand that it is possible to write more than one equilibrium constant for a particular reaction.

Given the following equilibrium constant
H2(g) + Br2(g) ⇌ 2HBr(g) Kc = 10^19
Work out the values for the equilibrium constants for these reactions:
a) 2 HBr(g) ⇌ H2(g) + Br2(g)

b) 2 H2(g) + 2 Br2(g) ⇌ 4 HBr(g)

c) ½ H2(g) + ½ Br2(g) ⇌ HBr(g)

What is the value of Kc of the overall reaction after combining the two individual reactions?
A(g) + B(g) ⇌ AB(g) Kc= 0.24
AB(g) + A(g) ⇌ A2B(g) Kc= 3.8

2 A(g) + B(g) ⇌ A2B(g) Kc= ?