When a radioactive sample decays for 2 half-lives the amount remaining will be of the original?

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

2b2t

explanation:

2b2t

b) nuclear ive learned that in a pedtrodic table