The molar mass for C is 12.011 and then you multiply that by 4 and you get 48.044. The molar mass for H is 1.008 and then you multiply that by 6 and you get 6.048. You add those together and you get the molar mass of C4H6, which is 54.092. You divide 53.39/54.092 and you get 0.987 moles C4H6.
