How is the element lead formed?

Natural formation of lead occurs by radioactive decay of uranium and thorium through radon (222Rn). Four stable isotopes are known, 204Pb, 206Pb, 207Pb and 208Pb, the first three of which are used for estimating the ages of rocks. Lead compounds exist mainly in +2 or +4 oxidation states, the former being more common.

it means there are 3 atoms of oxygen

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