I have created compound table but also wanted to find a formula to work out an equation of what someone will need to make each year

on their investments to hit a certain target.

For example: If Peter had £137,000 in savings and wanted to have £800,000 at retirement in 28 years, how much interest will he need to make

on his starting amount each year. The profits/interest will be reinvested every year.

Does anyone know the formula to work this out?