(x,y) = ( -(16/7), -(12/7) )
There would be 8 lines of symmetry for this shape.
To simplify the problem imagine the half-life was 2.5 minutes. This means that there would be 10/2.5=4 periods of halving the mass, which means 1/2⁴=1/16 of 18g=1.125g.
So for the given half-life we calculate 10/2.552=3.9185 approx. So we now find 2 to this power=15.1211 approx and divide into 18=1.19g. This is close to the rough estimate we did earlier.
800
There are 52 weeks in the year, so since 2 weeks are taken off, they only work 50 weekends a year, which is a total of 100 days. 100 days x 8 hours is 800 hours total