How far do I stitch?

My pattern says to “work straight until left front measures same as Back to shoulder shaping, finish after purl row.” The back portion was stitched 8 3/4 in. long and then it took five rows to cast off every stitch – eight per the first four rows and the remaining stitches on the fifth row. If I am working the front to the “shoulder shaping” am I only knitting until the point where I began casting off or to the total length of the back including the cast off rows?

Measure to the shoulder shaping.