The pollution level along a straight road between factories A and B, which are 10 km apart, is given by [math]p(x)=\frac{a}{x+1}+\frac{b}{11-x}[/math] where [math]0\leq x \leq 10[/math], where [math]x[/math] is the distance from Factory A, and [math]a[/math] and [math]b[/math] are positive constants. On Pi Day (March 14) the values of [math]a[/math] and [math]b[/math] are measured to be 9 and 4 respectively.
a) Determine the value of [math]x[/math] at which the pollution level is at a minimum.