The error is in the second step they subtracted 3 from both sides but it was a 3x, which you can not do.
Correction.
9x+18+3x=1
12x+18=1
12x=-17
x=-17/12
You will need to add all the dimensions together, also know as perimeter
The definition of two events being mutually
exclusive (or disjoint) only means that it is not possible for the two events to
occur together. Given two events, E and F, they are mutually
exclusive and also mean independent.
In this case, since events E and F are mutually
exclusive, therefore the probability that either E or F will occur will simply
be the sum of two events.
P (E or F) = P (E) + P (F)
P (E or F) = 0.25 + 0.51
P (E or F) = 0.76
Therefore this means that there is a 76% probability that
either E or F will occur.
He would need to exercise for approximately 14 minutes to get to 120 bpm
You're doing it exactly right! Keep on going! :)