Answer:
$7
Step-by-step explanation:
Your two equations are ...
Double the second equation and subtract the first:
2(2s +4t) -(4s +6t) = 2(42) -(70)
2t = 14 . . . . . simplify
t = 7 . . . . . . . divide by 2
The cost of each tie is $7.
Answer:
Area of shaded region = 134.13 square feet
Step-by-step explanation:
Area of the shaded region = Area of square - Area of circle

F=ar^t if the half-life is 96 years...
.5=r^96
ln(.5)=96lnr
ln(.5)/96=lnr
r=e^((ln.5)/96)
f=800e^(336(ln.5)/96)
f=70.71
So about 71mg will remain after 336 years.