The ornamental design for a mechanicalpencil with a lead tank, as shown and described.
FIG. 1 is a front view of the design according to the invention.
FIG. 2 is a right side view of the design according to the invention. The left side view is the same as the right side view.
FIG. 3 is a rear view of the design according to the invention.
FIG. 4 is a top plan view of the design according to the invention; and,
FIG. 5 is a bottom view of the design according to the invention.
The broken lines showing portions of the top and bottom in FIGS. 4 and 5 are included for the purpose of illustrating environment and form no part of the claimed design.