Answer:

First, plot the number of people who have all three cars:

Now, fill in the numbers of people who own two cars.  30 people said they own a Ford and a Mercedes.  You might ask yourself if these 30 people are in addition to the 21 who own all three cars or whether they include the 21 all-car-owners.  You could try it both ways, and then you'll discover a contradiction in one of them.  It turns out that the 30 people who own both a Ford and a Mercedes include the 21 who own all three cars.  So 30-21=9 people own just a Ford and a Mercedes.

Similarly, 47-21=26 people own just a Ford and a Jaguar,
and 35-21=14 people own just a Mercedes and a Jaguar.

There are 113 Jaguars, and 26+21+14=61 people own a Jaguar and some other car.  So 113-61=52 people own just a Jaguar.

There are 120 Mercedes, and 9+21+14=44 people own a Mercedes and some other car.  So 120-44=76 people own just a Mercedes.

There are 77 Fords, and 26+21+9=56 people own a Ford and some other car.  So 77-56=21 people own just a Ford.

A) How many people owned a Ford but nothing else?
You can read this right off the Venn diagram: 21.

B) How many people owned a Jaguar and a Ford but not a Mercedes?
Another one right off the diagram: 26.

C) How many people owned a Mercedes or a Ford?
For this one, you could add all six numbers from the diagram, but a quick look at question D tells you there's an easier way.  First, add up all the numbers on the diagram to see how many people were surveyed.

21+52+76+14+9+26+21=219 total people surveyed.

Now the people who owned a Mercedes or a Ford are the total minus those who owned just a Jaguar.  219-52=167.

D) How many owned a Ford or a Jaguar?
The total minus the number owning just a Mercedes is 219-76=143.

E) How many did not own a Ford?
The numbers that lie outside the Ford circle are 52+14+76=142.

F) How many owned a Jaguar and a Mercedes but not a Ford?
Read it right off the diagram: 14.

G) How many owned a Mercedes or a Jaguar but not a Ford?
Is this question different from E?  I don't think so.  142.