You buy $100$ shares of stock ABC today with a market order. The limit order book at the time of your trade is as follows:

$\backslash$table$[[$Order type,Price,Quantity$],[$Ask$,$$$15\mathrm{.}0,80],[$Ask$,$$$13\mathrm{.}5,60],[,,],[$Bid$,$$$12\mathrm{.}0,60],[$Bid$,$$$11\mathrm{.}5,60]]$

a$.$ What is the bid$-$ask spread?

b$.$ What is the average price you pay for the stock?

c$.$ Continuing on the the previous example, assume that you sell the $100$ shares in six months. At that time, the order book is as follows:

$\backslash$table$[[$Order type,Price,Quantity$],[$Ask$,$$$16\mathrm{.}0,120],[$Ask$,$$$15\mathrm{.}5,30],[,,],[$Bid$,$$$14\mathrm{.}0,80],[$Bid$,$$$12\mathrm{.}5,60]]$

The stock has also paid a dividend of $$1$ per share during this period. What is the total return $($in percent$)$ on your position?