A triangle has sides 6 cm, 11 cm and x cm and its area is 30 cm2. Which of the following equations in x correctly represents this condition?
a) 217+x(217+x−6)(217+x−11)(217+x−x)=30
b) 217+x(217+x−6)(217+x−11)=900
c) 217+x(217+x−6)(217+x−11)(217+x−x)=900
d) (6+11+x)((6+11+x)−6)((6+11+x)−11)((6+11+x)−x)=900