First you get 7.83 kPa = 7.83 * 10^4 Pa
Then convert it to atm by using the relation 1 Pa = 9.8692 * 10^-6 atm, this gives you
7.83 kPa = 7.83 * 10^4 * 9.8692 * 10^-6 atm
= 77.275836 * 10^-2 atm
= 0.77275836 atm
Now round to three significant digits,
= 0.773 atm
