in triangle PQR, PQ=(x+2)cm, PR=(5-x)cm and <QPR=30. the area(A) of the trangle is 1/4(10+3x-x^2)

the question i am struggling with is this; "use the method of completing the square to find the maximum value of A and the corresponding value of x."

i'd be grateful for someone to explain how its done and to also say what is done if it is a minimum value in case that another question asks me to find the minimum. thanks MHF.