The ornamental design for an automotive seatmountabletabletcomputer holding device, as shown and described.
FIG. 1 is a perspective view of a new and ornamental automotive seat mountable tablet computer holding device;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a first side elevation view thereof;
FIG. 5 is a second side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a perspective view thereof mounted on an automotive seat and holding a tablet computer, the seat and counter being shown in phantom for environment only and forming no part of the claimed design, and the dash-dash lines shown in the figures are claimed stitching.