If the demand function for a commodity is given by the equation p2 + 12q = 1800 and the supply function is given by the equation 900 − p2 + 6q = 0,

Question

find the equilibrium quantity and equilibrium price.

Answer 1

I will assume your two equations are
p^2 + 12q = 1800 and 900 − p^2 + 6q = 0
p^2 + 12q = 1800
− p^2 + 6q = -900
add them:
18q = 900
q = 50

plug into p^2 + 12q = 1800 and use the positive answer to p