Lucky for you (as is the case with many of the lower-stroke kanji), this kanji is the same as the radical you've already learned. The radical that makes up this kanji is seven and the kanji (which is exactly the same) is also seven. So, if you know the radical, you know the meaning of the kanji as well.
You know this kanji means Seven, so let's use that to remember the reading too. Seven is a lucky number, usually, but this time it wasn't so good.
Seven percent is all she got on her test after she cheated (しち) on it.