Percentage

A company calculates the prices of jobs by adding overheads to the prime cost and adding 30% to the total costs as a mark up. Job j256 was sold for £1690 and incurred overheads of £694. What was the prime costs of the job? Answer : Selling price 1690 Less profit margin (30/130) 390 Total cost of job. 1300 Less overheads. 694 Prime cost. 606 I can work backwards and understand 30% of 1300 but how do you work out the 30 percent using the information in the question. I can't get to the 390 as the profit margin.