7 is either A or B and 8 is D.
You must look in between the primary colors.
In between blue and yellow, there will be three colors but the one in the middle is the complementary (Green)
It depends if it's a single or a double bar line.
if it's a double bar line it's just there to separate the sections of the music and if it's a single bar line all it does it separate the beats in order to make a measure.
