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.
X+y=23
X-y=7.4
X+y=23
y=23-X
X-y=7.4
(23-y)-y=7.4
23-2y=7.4
-2y=-15.6
Y=7.8
X+y=23
X+7.8=23
X=15.2
Therefore the two numbers are 7.8 & 15.2
Since we have two possible pieces of information and 2 items to solve for, we know this is a system of equations.
Our first piece of information is that our shorter leg (s) is 2 feet shorter than our longer leg (l). This can be written as s=l-2.
Our second piece of information is that using the Pythagorean theorem that our shorter leg squared plus our longer leg squared is equal to our hypotenuse squared. This can be represented by s^2+l^2=10^2. Now we can solve.
We have already isolated for s in our first equation, so we can substitute l-2 in.
(l-2)^2+l^2=10^2
l-2+l=10
2l-2=10
2l=12
l=6
Now we can substitute in for s in our simpler equation
s=6-2
s=4
We now know that using our knowledge of systems of equations, the side lengths of this right angle triangle are 6 and 4.