At a certain amusement park, there is a bulk discount for tickets. If you buy up to 60 tickets in one order, the price for each ticket is $\$70$. However if you buy more than 60 tickets in a single order, the price of every ticket is reduced by $\$1$ for each additional ticket bought. If $t$ is the number of tickets bought in bulk at one time, what is the largest $t$ which will bring the amusement park a profit greater than $\$4200$?
