mia has a certain amount of money. if she buys $4$ pens and $1$ pencil, she will have $\$5$ left over. if she buys $2$ pens and $2$ pencils, she will have $\$3$ left over. if edward arrives with the same amount of money as mia, together they can buy $7$ pens and $4$ pencils and spend all their money. if $a$ is the cost of one pen and $b$ is the cost of one pencil, compute the ordered pair $(a,b)$.
