You need to determine the value of the vehicle at the end of the lease (some quoting websites will provide this) and subtract that from the retail price and then subtract the down payment.
Take that value and divide by the term of the lease.
630 * 48 = $30,240 + $5,000 = $35,240
So either it is worth nothing at the end of 48 or a high rate. How many miles a year?