Given:
Polynomials
To find:
Monomial of 2nd degree with leading coefficient 3
Solution:
Monomial is an algebraic expression with only one term.
Option A: 
It is not a monomial because it have 2 terms.
It is not true.
Option B:
It is not a monomial because it have 2 terms.
It is not true.
Option C: 
It have one term only. So, it is a monomial.
Degree means highest power. So degree = 2
Leading coefficient means the value before variable.
Leading coefficient = 3
It is true.
Option D: 
It have one term only. So, it is a monomial.
Degree means highest power. So degree = 3
It is not true.
Therefore
is a monomial of 2nd degree with a leading coefficient of 3.
Well the formula is : b1+b2/2 (h)
so the height would be solved as :
13.5 = 3+6/2 (h)
13.5 = 9/2 (h)
h = (13.5)/(9/2)
h = (13.5) x (2/9) *reciprocal*
h = (27) / (9)
h = 3
Multiple 15 by 6, the answer is 90 square cm
B has the pair that are vertical angles