To calculate P(at least one valve opens), we can find 1 - p(no valves open).
This is equal to 1 - (0.05)^5, or 0.9999996875.
P(at least one valve fails to open) is equal to 1 - p(all valves open and none fail). This is 1 - (0.95)^5, or 0.2262190625.
I would go with C because if you do A then its all new students and thats one view D is the same. C seems like the best choice.
You olny do the problem in some u need to reduce
11-

Taking y to the other side;
11-3-6x=

8-6x=

Multiply each side by 2
16-12x=y
y=16-12x