B=(c-3a)/2
Should be the equation you get
For those unaware of what this means
This is part of the thousands of reviews for a seafood place in China. Don't believe me? Look it up!
A door alarm works in 72 out of 100 cases.
surveillance camera works in 68 out of 100 cases.
The probability that method A is used = 72/100
The probability that method B is used = 68/100
Since both method are used we find the probability of A and B
Probability ( A and B) =
* 
=
Angle A = arctan(12/5) = 67.4 degrees
Angle A = arccos(5/13) = 67.4 degrees
yes the answer was the same