Explanation:
Find lower quartile first: 1/4 (61)th term which equals to 15.25th term. Use your graph to estimate where 15.25 is and draw a line till it meets tne curve. As soon as it touch the curve, continue the line downward and you'll get LQ in kg. Secondly, find upper quartile: 3/4(61)th term which equals to 45.75th term. Proceed the same thing I mentioned above for lower quartile. Then the formula for interquartile range is upper quartile minus lower quartile and you'll get the answer in kg.