We first compute the no. of moles of each element in the compound. So first, the C is said to have 85.7% by mass in the solution. So we solve: (0.857 g C)(1 mol C/12 g C) = 0.0714 moles of C. Then next we solve for the moles of H. We follow the same procedure: (0.143 g H)(1 mol H/1 g H) = 0.143 moles of F. Next we compute the total number of moles: 0.143 + 0.0714 = 0.2144 moles. Next we divide each moles of the elements to the total number of moles to get the formula: C --> 0.0714 mol/0.2144 mol = 0.333 or (1/3) and for H --> 0.143 mol/0.2144 mol = 0.666 or (2/3). So we multiply both by 3 to have a whole number, so we have: 3[C(1/3)H(2/3)] = CH2.