Amineral consisted of 29.4% calcium, 23.5% sulfur and 47.1% oxygen. what is the empirical formula?

Step  one  calculate  the  moles  of  each  element
that  is  moles= %  composition/molar  mass
molar  mass  of    Ca  =  40g/mol,     S=  32  g/mol ,   O=  16 g/mol

moles  of      Ca = 29.4 /40g/mol=0.735 moles,      S= 23.5/32  =0.734 moles,  O= 47.1/16= 2.94   moles

calculate  the mole  ratio  by  dividing   each  mole with  smallest  mole   that   is  0.734
Ca=  0.735/0.734= 1,      S=  0.734/0.734 =1,   O  = 2.94/  0.734= 4
therefore  the  emipical  formula  =  CaSO4

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

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