Retirement deed safeguards

Partner A and Partner B started a partnership with equal working capital in January 2014. Then Partner B could not bring more funds and Partner A had to step in and contributed 95% of the capital by 2017. Partner A was sleeping partner (not mentioned in deed, just understood). However, Partner A found that the firm was making profits which were not being disclosed by Partner B. So Partner A decided to withdraw from the firm and Partner B agreed to return the working capital and bring in another partner. Questions: 1) Partner A is completely unaware of how the firm was being run. He had given Power of Attorney to Partner B to conduct the business. So what are the safeguards he needs to specify in the retirement deed so that he will not be liable for anything in the future. 2) The partnership deed contained the following clause - "firm shall pay interest @ 12% per annum, to the partners on the amount of capital contribution or loans advanced by each of them respectively and the profits or losses of the business of the firm shall be arrived at after accounting for the interest so payable as a business expenditure of the firm". The deed does not specify whether the interest payable is simple interest or compound interest. Is there any legal precedent or stipulation which can clarify this so that partner A can claim the correct amount? Thank You