A mixture of four gases exerts a total pressure of 960 mm Hg. Gase A each exert 120 mm Hg. Gas B exerts
50 mm Hg. What pressure is exerted by gas C?

Omitted question:I think you mean Gas A and D each exert 120 mm Hg, if Gas D has a different value , just lug it into he equation as shown below and solve.

Gas C= 670mmHg

Explanation:

According to Dalton law of partial pressure

The total pressure of a mixture of gases is the sum of the pressures of each gas and can be illustrated as

Pressure total=P1+P2+… +Pn.

Total Pressure = Gas A + Gas B + Gas C + Gas D + Gas...

Now we have

Total Pressure = 120 mm Hg + 50mm Hg + Gas C + 120 mm Hg

960mmHg = 120 mm Hg + 50mm Hg + Gas C + 120 mm Hg

960mmHg =290mmHg +Gas C

Gas C =960mmHg -290mmHg

Gas C= 670mmHg

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.