As said, the isogonic lines on the chart are the place to get the correct magnetic variation value. I don't know what one is supposed to do on a test question if the appropriate partial chart is not shown, or the line is not readable.
As an in-depth technical aside: VOR magnetic variation listed with Navaid info in the A/FD (now called "Chart Supplement"), and/or the VOR compass rose depicted on a chart will NOT give you the correct mag. var. number. As the variation changes over time (due to pole drift), they may or may not keep up with re-aligning the VORs, so there may be a lag of several years difference between the degrees shown on an isogonic line and the degrees offset of a VOR. Probably wouldn't make a difference if you're trying to eyeball an angle during flight, but your test answer measured with a plotter could be many degrees off.
In my neighborhood, the most recent isogonic line shows 10 deg. 30 min. E variation. There are 3 VORs nearby, all nearly right on the charted line, and they have variation listed as 10E, 16E, and 13E. Obviously, the 1st has been recently re-aligned, while the 2nd has not been reset for many years. (RIW, BOY, and WRL on the Cheyenne sectional, if anyone is still interested.)