You are interested in borrowing $$10,000$ for one year by using a box spread.

You are given the following option prices:

$\backslash$table$[[$Strike price,Call premium,Put Premium$],[30,8\mathrm{.}06,1\mathrm{.}31],[40,3\mathrm{.}13,5\mathrm{.}80]]$

The continuously compounded risk$-$free interest rate is $0\mathrm{.}06.$

One unit of the box spread consists of a long $30-40$ bull spread of calls and a long $40-30$ bear spread of puts.

Calculate the number of units of the box spread needed to achieve the financing goal, and determine whether they are bought or sold.