I think you mean x2+7x-18 which factorises into (x+9)(x-2).
x2+7x+18 has no real factors, that is, the factors are complex, involving imaginary numbers. I don't think Algebra 1 curriculum includes complex numbers.
The question doesn't say what is required of the given expression, so I have only assumed that factorisation was requested. For example, it could be asking the value of the expression when x has a certain value; or it could be asking what it's graph looks like; or it could be asking what is the vertex of the parabola it represents; etc.