The length of the completed tunnel can be calculated using the equation. If the project will be completed 86 days after the TBM was introduced, the length of the completed tunnel will be feet.

The y - intercept of an equation is the value of y when x is substituted with zero. From the given equation,

y = 25x + 225

Substituting,

y = (25) (0) + 225

y = 225

Thus, the y - intercept of the given equation is 225.