Solve the following system using substitution:

y = x + 2
y = 3x
I don't understand this question.

Substitute 3x for y in the first equation.

That leaves you with
3x = x + 2
which can be rewritten
2x = 2

Solve that for x.

Then, knowing x, use either equation to get y.

Answer (1,3)

Yes, that is the answer. x = 1 and y = 3

Simplify (d^4)(d^5)^3.

Is it d^27

Yes

Sum of the solutions to

x2 - 3x - 18 = 0

Is it -3 ?

no,

for ax^2 + bx + c = 0, the sum of the roots is -b/a
so the sum is -(-3) = +3