Answer:
Optical axis
Step-by-step explanation:
Optical axis is the rotational symmetry axis of the surfaces.
A line with a certain degree of rotational symmetry is called as the optical axis in an optical system.
It is the straight line that passes through the geometric center of the lens and joins two curvature centers of its surfaces.
It is also called as the principal axis.
The answer is 18. Just take the number that comes later and simply subtract from the original number. EXAMPLE- 138-120=18. Hope this helps.
Slope intercept form is y=MX+b.
M is the slope, x is the x intercept, and b is the y intercept
the slope is

An intercept is where the formula crosses the axis. therefore, the x intercept is .5, and the y intercept is 1
so the point slope formula is
I believe $30 but i am not completely sure :)