Answer:
415.47
Step-by-step explanation:
The answer is 51 because 180-139=51
Initial amount,
.
Final amount,
.
Time taken, t = 6:00 - 2:00 = 4 hour.
We know,

Therefore, the half-life of the isotope is 1.024 hours.
Hence, this is the required solution.
<h2>⇛ <u>A</u><u>N</u><u>S</u><u>W</u><u>E</u><u>R</u><u> </u>⇚</h2>
<h3>2x - y = 0 </h3><h3>x + y =-3 </h3><h3> is matched with </h3><h3>[ O -1 ] (system determinant)</h3><h3>[ 3 1 ] ( y - determinant )</h3><h3> ( x - determinant )</h3>
<h2>HOPE U UNDERSTOOD !!!!(:</h2>