Answer is 456 mmHg.
Explanation;
This is a simple unit conversion problem.
1 atm = 760 mmHg
Hence,
0.600 atm = (760 mmHg / 1 atm) x 0.600 atm
= 456 mmHg
Pressure can be measured by using many units such as atm, Pa, torr, bar, cmHg, mmHg and so on.
The relationships among those units as follows
1 atm = 101325 Pa = 1.01325 bar = 760 torr, 760 mmHg = 76 cmHg