The magnitudes of enthalpy of combustions of $C{H}_4,C_2{H}_6,C_3{H}_8$  and n-butane in $kJmo{l}^{-1}$ are 890, 1560, 2220 & 2879 respectively. The ratio of enthalpies of combustion of n-heptane to that of ethane rounded off to nearest integer is______.

The differencesin enthalpy of combustionsbetween adjacent members given are 670, 660 &659 respectively. i.e, adjacent members differ approximately by about 660.
Magnitude of enthalpy of combustion of n-heptane will be about  $2879+3\times 660=4859$