You can put this solution on YOUR website!
You have the correct value for f(3) since
f(x) = 3x^2+4
f(3) = 3(3)^2+4
f(3) = 3(9)+4
f(3) = 27+4
f(3) = 31
We replaced x with 3 and evaluated
A similar idea will happen with the next part. Let's first find f(-x)
So,
f(x) = 3x^2+4
f(-x) = 3(-x)^2+4 ... replace every x with -x
f(-x) = 3x^2+4 ... note how (-x)^2 = x^2
This is because the -x really means -1x, and we're squaring -1 to get +1 or just 1.
Now we multiply both sides by 3 to get...
f(-x) = 3x^2+4
3*f(-x) = 3*(3x^2+4)
3*f(-x) = 3*(3x^2)+3(4)
3*f(-x) = 9x^2+12
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