The Simpsons are moving into their new home. They purchased it for $$250,000$ by putting a down payment of $$120,000$ towards the purchase and paying the balance with a $$130,000$ mortgage amortized over $20$ years at $6\mathrm{.}75\%$ per annum $($for a $3-$year term$).$ At the end of the $3-$year term, the interest rate increased by $0\mathrm{.}5\%.$What is the approximate increase in their monthly payment?