Casting on sleeves for a sweater

I am trying to cast on sleeves instructions state:
Row 1: cast on 34 sts, knit to end of row 128 sts.
Row 2: cast on 34 sts, purl to end of row 162 sts.
When i was doing the back of the sweater i was working with 94 sts. So do i cast off after i am done with the back of the sweater, cast on 34 sts and then sew the back and sleeves together?

No, you can cast on with the working yarn and work back across on the next row. There are a couple of ways to do that depending on what you like. A lot of people use backward loop, I use that variation that makes little half-hitches over the needle, some people knit on the extras–there are other ways, too.

When you get the extras cast on, you work them just the way you usually do, then the body stitches, then cast on the other side’s stitches.

Nobody ever notices the difference in the first and second sides, because most of the time the pattern has you cast off the first sleeve first.