what is the molarity of the acid in when a 30mL sample of HCl is titrated with 10mL of 6M NaOH?

HCl + NaOH ==> NaCl + H2O

mols NaOH = M x L = ?
mols HCl = mols NaOH (look at the coefficients in the balanced equation.)
M acid = mols acid/L acid.