142 g/martini x 2 martinis = 284 g.
284*0.30 = about 85 g alcohol
85*0.15 = about 13 g alcohol in the bloodstream.
What's the density of blood? I guess we assume 1.0 g/mL so 7 L will be 7,000 mL or 7000 g. So the person has 13g in 7013g total or %alcohol = (13/7013)*100 = about 0.19% which is 0.19g/100 g = about 0.0019 g/mL.
All of these numbers are estimates; you should confirm them on your own. Draw you conclusions from your final answer.