What the
law of conservation of mass means.

the law of conversation says that mass in an isolated system is not created or destroyed by chemical reactions or physical transformations.

? you expect us to answer this? ? this is your schoolwork, i don't think we can with this, i think it would considering being

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