Snell's law relation for air glass boundary is given by equation `n_(air) sin theta_(1) = n_(glass) sin theta_(r)`. Here angle of refraction in glass is `theta_(r)` and the angle of incident in air is `theta_(i)`. The refractive index of air is `n_(air)=1` (with negligible uncertainty). In an experiment to verify Snell's the best fit line on a graph between `sin theta_(r)` (on the y-axis) and `sin theta_(i)` (on the x-axis) is given by the eqyuation `y=(6.66pm0.05)xx10^(-1)x+(0.022pm0.024)`. The refractive index of the glass, including the error is reported as `1.abpm 0.0c`, where a,b and c are digits after tje decimal point. Calculate value of `(a+b-c)`.