You can put this solution on YOUR website! log3(z+1) = 2 if and only if 3^2 = z+1 which becomes 9 = z+1 which becomes z = 8
that should be your answer.
replace z in your original equation and you get log3(8+1) = 2 which becomes log3(9) = 2 which is true if and only if 3^ = 9 which is true, so the solution of z = 8 is good.
