(a) The
x-axis intercept represents where the discharge reaches 1.0 V (ln 1 =
0).

Use the equation:

(1.0 V ÷ 6.0 V) =
*e*^{-t/22s}

Taking natural
logs:

0 - ln (6.0) = -
*t* ÷ 22 s (minus signs cancel out)

*t* = 1.792
× 22 s = 39.4 s

This is
consistent with the *x*-axis intercept.