Answer:
P=1/42.
Step-by-step explanation:
We know that the student council has 10 members where 5 of the members are Seniors. They need to choose a President, Vice President, Secretary and Treasurer. We calculate the probability that the President is a Senior:
We calculate the number of possible combinations:

Number of favorable combinations is 5.
Threfore, the probability is
P=5/210
P=1/42.
We use unitary method over here. To find out the number pages he writes in 1 hour we should;
16÷8 = 2.
So Brennan writes 2 pages in 1 hour.
Hence, in 10 hours he writes;
2 × 10 = 20.
∴ in ten hours Brennan writes 20 pages.
X+2y=4
3x-2y=4
4x=8
x=2
2+2y=4
2y=2
y=1
y=1
x=2
Hope this helps :)