Your "h (x)=x 2 squared +6x-3" is ambiguous. If you meant "x squared," then you need only write x^2 OR "x squared," but NOT "x 2 squared."
I will assume that by "h (x)=x 2 squared +6x-3" you actually meant:
h(x)=x^2 +6x-3. To find h(3), subst. 3 for x: h(3) = (3)^2 + 6(3) - 3, or
h(3) = 9 + 18 - 3, or h(3) = 24.
