Try your best and the website tells me if you are right or wrong once i submit it so be honest. you

Let's look at the first section. You would need to figure out how much both cost per bar. 
10-pack: $15.37 ÷ 10 = $1.537
12-pack: $15.35 ÷ 12 = $1.27916666667

The 12-pack is the cheapest per bar. 

Now, let's look at the second section. You would need to figure out how much a single ounce would cost. 
10-pack: $15.37 ÷ 10 = $1.537 ÷ 2.1 = $0.7319047619
12-pack: $15.35 ÷ 12 = $1.27916666667 ÷ 1.4 = $0.91369047619

The 10-pack is the cheapest per ounce. 

The lower price per bar would be the 12-pack. 
The lowest price per ounce would be the 10-pack. 

I hope this helps!