I think I have found the right answer but if someone could have a look at it for me, that would be awesome. Thanks.

The John Deere company has found that the revenue from sales of heavy-duty tractors is a function of the unit pricep,in dollars, that it charges. The revenueR,in dollars is -.05p^2 + 1900p

At what prices p is revenue zero? Round to four decimal places.I have when revenue is zero, then p=0 or 3800. (0,0) and (3800,0)

For what range of prices will revenue exceed $1,300,000? Round to four decimal places.

886<p<2904 The price must be between or equal to the values of $886 and $2900 for revenue to exceed $1,300,000.

For this part, I just looked on the table of my calculator. Should I be more precise and use a formula?