x: x-value whose matching y-value should be forecast
known_ys: known y-values
known_xs: known x-values
This function estimates a future value according to existing values using simple linear regression.
If known_xs or known_ys contains no data entries or different number of data entries, this function returns a #N/A error. If the variance of the known_xs is zero, this function returns a #DIV/0 error.
This function is Excel compatible.