We first need to write the function in standard form.
y = -x^2 - 7x + 18
To find the axis of symmetry, we do -b/2a
The a and b are the coefficients of the x values.
So a would be -1 since -x is same as -1x
Follow that, b would be -7.
Then just plug the values in. - (-7)/2(-1) = -7/2
The axis of symmetry is -7/2