Preparation of Triphenylmethanol?

For my organic chemistry lab, I am asked to find the LIMITING REAGENT between either phenylmagnesium bromide and methyl benzoate. This is the stoichiometric equation that I figured out for the experiment: 2C6H5MgBr + C6H5COOCH3 ----H2SO4----> (C6H5)3COH + CH3OH + 2Mg + SO4 + 2Br. The moles given for C6H5COOCH3 is 0.045 mol. The problem is that I am only given the moles of Mg which is 0.1 mol and C6H5Br which is 0.12 mol separately. How do I find the moles of phenylmagnesium bromide when I am only given the individual moles of its initial reactants before any reaction occurred???