8 < 2b
8/2 < b
4 < b
2b + 15 < 5
2b < 5 - 15
2b < -10
b < -10/2
b < -5
answer is : b > 4 or b < -5
85% if the questions. You would take 68 and divide it by 80 to find the percentage of answered questions.
The answer is A(3). 3 arcs will be drawn

Using the fact that cos is 2π-periodic, we have

That is,
for any
and integer
.

We get 2 solutions in the interval [0, 2π] for
and
,
