How can i improve this paragraph?

Hi, I am practicing the writing section of IELTS test. Please share your comments and critics.

The question shows me three pie chart showing a school expenditure in 1981,1991,2001 and requires me to summaries the information by sectioning main features and making comparisons. Please assume that the data i have taken is correct.

The changes and variation in annual spending of school in being studied here for period of 1981 to 2001.Teacher's salary which is the most expensive part of school administration accounted for 40% of total expenditure in 1981. It increased to 50% in 1991 and then reduced to 45% in 2001. Insurance which was merely 2% and 3% of total expenditure in 1981 and 1991, increased to 8% in 2001. Other worker's salary reduced constantly from 28% to 15% between the same period. Resources such as book saw marginal increase from 18% to 20% between 1981 to 1991 dipped to 15% of total expenditure in 2001. Lastly, furniture equipment accounting 15% in 1981, saw 10% reduction in 1991 but shot back to 23% of total expenditure in 2001.

Few doubts i have

1. The question says minimum of 150 words. These are only 100. How could i have further elongated it?

2. Is it ok to use % symbol? or do i need to write "percentage"

I am thankful for your time and efforts:D