The excluded values are the values that the variable cannot take on because it makes the overall expression undefined.
For example, we can't have [tex]x=0[/tex] in the expression [tex]\dfrac1x[/tex] because [tex]\dfrac10[/tex] is undefined.
For both of these problems you do the same sort of thing, with some factorization along the way:
[tex]\dfrac{9p^2}{4p^2-12p}=\dfrac{9p^2}{4p(p-3)}[/tex]
If [tex]p=0[/tex] or [tex]p=3[/tex], the denominator is 0 and we have an undefined expression, so these are the excluded values.
[tex]\dfrac6{m^2+m-42}=\dfrac6{(m+7)(m-6)}[/tex]
If [tex]m=-7[/tex] or [tex]m=6[/tex], we get an undefined expression.
