Corresponding angles are always congruent.
I believe the answer is A "If a triangle is equilateral, then it has three congruent angles". Hope this helps!
The formula for half-life is:
A is the amount remaining, P is the initial amount, t is the time that has passed, and h is the half-life of the substance. Plug in the values that you know and solve:
Rounded to the nearest whole number, the density of the substance was about 13<span>mg / cm².</span>