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Hey there! Alright so this is very easy, I'll explain everything no worries. First you need to take both of the reactants and react then to find out how much product each can make, whichever makes the least amount is the limiting. To do this you simply convert the given grams of each reactant into moles by using their molecular weights, then you look at the balanced equation and do a mole to mole comparison, this way moles of reactant is canceled and you have moles of product. Since they want the theoretical yield of PbCl2, you need to further covert moles to grams, again by using molecular weigh of PbCl2. The amount that the limiting reactant can make is your theoretical yield. After that its pretty easy to find percent yield, just use the equation for it. You were given the actual yield, you just found theoretical. And thats it. Hope you find this helpful. Let us know if you have any more question about this.