Answer
One head of lettuce should be sold for 1.15 dollars.
Work Step by Step
Let s represent the selling price.
We can use the following guideline to solve this problem:
Selling price = Cost + Profit
s = 0.50 + 130% $\times$ 0.50
s = 0.50 + 1.3 $\times$ 0.50
s = 0.50 + 0.65
s = 1.15
One head of lettuce should be sold for 1.15 dollars.