If the incomes of companies A and B in 2013 were in the ratio 3 : 4, then the expenditure of company A was what per cent less than that of company B in that year (correct to one decimal place)?

We will assume the incomes of companies A and B in 2013 to be 300 and 400 respectively.
Profit for Company A and B are 45% and 30% respectively.
Profit % = $$\frac{Income\ -\ Expenditures}{Expenditures}\times\ 100$$.
This gives the expenditures of Companies A and B as 206.8 and 307.6 respectively.
Percentage by which A's expenditure is less than B's expenditure = $$\frac{307.6-206.8}{307.6}\times\ 100\ =\ 32.79\%\approx\ 32.8\%$$.