Part A: For the following systems at equilibrium A : 2NOCl(g) ⇌ 2NO(g) + Cl2(g)
B : H2(g) + I2(g) ⇌ 2HI(g)
Classify these changes by their effect.

Leftward shift - system A decrease container size
No shift - system B increase container size and system B decrease container size
Rightward shift - system A increase container size

Part B: For the following systems at equilibrium
A: CaCO3(s) ⇌ CaO(s) + CO2(g) ΔH = +178 kJ/mol
B : PCl3(g) + Cl2(g) ⇌ PCl5(g) ΔH = -88 kJ/mol
Classify these changes by their effect.

Leftward shift - system C decrease temperature and system D increase temperature
No Shift - N/A
Rightward shift - system C increase temperature and system D decrease temperature

Both of them I was able to figure out, but I want to know how or why those are the solutions to the questions? I ask this because I answered some wrong, until I guessed it, and I got it right.