Decisions regarding the placement of code switch indicators depends on whether the math is embedded or displayed. Guidelines have been developed in order to strive for consistency. If the pdf example you posted is the same as the B2K file (which cannot be opened in this forum--it needs to be a BRF file), it looks like this might be a displayed expression because your runover line is indented two cells. The preferred layout for a displayed math expression that requires a code switch immediately before and immediately after is that if both switches do not fit on the same line as the expression, the opening switch should be placed at the end of the preceding text. This means that the first cell of the displayed expression will be the math, not the code switch indicator. Flexibility is built in to this guideline depending on pagination issues that are more of an concern when transcribing short documents such as worksheets.
In an embedded format, if only one of the code switches will fit on the line with the math there is no preferred placement. Having said this, however, general transcribing practice is to use as much of the line as possible before beginning a runover line, which means in the case of your example the opening switch may fall at the end of the previous line of text if it fits there.