a) The two parts of this expression, +2a and +5a are called terms and
the numbers in front of the variables, +2 and +5 are called coefficients.
Because the variables, a and a, are identical,
the two terms in this problem are called like terms.
Like terms can be added together by simply adding their coefficients.
So in this problem, since 2 + 5 is 7, 2a + 5a is simply 11a.
b) Since both terms contain an x, we can subtract them.
Also, change the minus to plus a negative.
So we have 12x + -3x which simplifies to 9x.
c) If there is no coefficient in front of the variable, you can give it
a coefficient of 1, so -p can be thought of as -1p.
So we have 3p + 2p -1p which is 4p.
