M + 12 = 10 solve equation

OK.  Watch carefully, as I guide you through the mysterious and
complex methods of solution, taught to me from the ancient
sacred scrolls of Tibet.  It won't be easy, but I'll go slow so that
neither of us gets lost along the path, to the ultimate wisdom. 
Remember ... the "solution" is the number that 'M' must be, in order
to make the equation a true statement.  Ready ?  Here we go. 
Fossen your seat belt, it's goin to be eh boompy rade, mon:

The equation.           You said that    M + 12  =  10

Subtract  12  from each side:            M          =   -2 .

Were you able to follow all of that ?

Gotta be d the music of previous eras

Num of plants = (original#ofplants)*(1.6)^t