In this case, since HCl and Pt react according to the following chemical equation:
Whereas PtClx is the compound containing Pt and Cl; thus, since 1.018 g out of 1.778 g correspond to Pt and therefore 0.760 g to chlorine, so we determine the empirical formula of this compound by firstly computing the moles of each element:
Now, we divide the each moles by those of Pt as the fewest ones in order to compute their subscripts in the empirical formula:
Well the width is 0.20 meters. Since there are a hundred centimeters in a meter, we just have to move the decimal point two times to the right to get a 20 centimeter width.