The answer is -1/3.
What you can do is substitute the botton "M" with 5p+8
so it would turn out to be 5p + 8= -10p + 3. You then add 10p to each side resulting in 15p + 8 = + 3. You then minus the 8 resulting in 15p= -5. So you then divide -5 by 15 resulting in p=-1/3
