Answer:
63
Step-by-step explanation:
This is because 25% of 84 is 21. He knows how to play 21 songs. 84-21=63.
63 is how many songs he does NOT know how to play.
Keep in mind that you can gather only like terms. Two terms can be summed/subtracted if they involve the same powers of the same variables.
So, going point by point:
you would have to do 170/20 which equals 8.5 multiply that by 8
so his daily does would be 510 milligrams
10 I think