Question

The mass of a particular substance is known to grow exponentially at a rate of 12.5% per week. Its initial mass was 34 grams and, after t weeks, it weighed 143 grams.
The equation modelling this growth is
34×1.125 t  =  143.
Use the method of taking logs to solve this equation for t, giving your answer correct to the nearest week.

(Your answer should be a number, without units)