[tex]\bf \begin{array}{|c|ll} \cline{1-1} \textit{a\% of b}\\ \cline{1-1} \\ \left( \cfrac{a}{100} \right)\cdot b \\\\ \cline{1-1} \end{array}[/tex]
so the tank tops are 70% off, meaning, 100% - 70% = 30%, the price you pay for one is just 30% of the regular price, if we put that in decimal that'd be (30/100), or just 0.3.
since the price of a tank top is "t", then for 2 is 2t, and the discounted price will just be 30% of "t" so (0.3)2t.
we now the t-shirts are each one 12 bucks discounted already, so for 3 of those will just be (3)(12).
the jeans are half off, namely 50% off, if we put that in decimals, that'd be (50/100) or just 0.5.
we know the regular price of the jeans is "j", so the discounted price will just be (0.5)j, and for just one well, (0.5)(1)j or just 0.5j.
