To solve this equation, start by noticing that you want to find t when P is 75%, or 0.75. Plug in 0.75 for P. Please see the attached screenshot for a step-by-step. The correct answer is 29.496 days.
EDIT 2: I actually was correct! You check the answer by substituting 29.496 for t in the original equation set equal to 0.75. It is 0.75. I had forgotten the negative sign when I checked.
EDIT 2: I actually was correct! You check the answer by substituting 29.496 for t in the original equation set equal to 0.75. It is 0.75. I had forgotten the negative sign when I checked.