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!