Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. IX. SN 1989B in NGC 3627

(Abridged) Repeated imaging observations have been made of NGC 3627 with the HST in 1997/98, over an interval of 58 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the prototypical, `Branch normal', type Ia supernova SN 1989B. A total of 83 variables have been found, of which 68 are definite Cepheid variables with periods ranging from 75 days to 3. 85 days. The de-reddened distance modulus is determined to be (m-M) ₀= 30. 22+/-0. 12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure. The photometric data of Wells et al. (1994), combined with the Cepheid data for NGC 3627 give MB (max) = -19. 36+/-0. 18 and MV (max) = -19. 34+/-0. 16 for SN 1989B. Combined with the previous six calibrations in this program, plus two additional calibrations determined by others gives the mean absolute magnitudes at maximum of = -19. 48+/-0. 07 and = -19. 48 +/-0. 07 for `Branch normal' SNe Ia at this interim stage in the calibration program. The second parameter correlations of M (max) of blue SNe Ia with decay rate, color at maximum, and Hubble type are re-investigated. The dependence of on decay rate is non-linear, showing a minimum for decay rates between 1. 0< Delta m₁5 <1. 6. Magnitudes corrected for decay rate show no dependence on Hubble type, but a dependence on color remains. Correcting both the fiducial sample of 34 SNe Ia with decay-rate data and the current 8 calibrating SNe Ia for the correlation with decay rate as well as color gives H₀= 60+/-2 (internal) km/s/Mpc, in both B and V. The same value to within 4% is obtained if only the SNe Ia in spirals (without second parameter corrections) are considered.