Answer:
20.25
Step-by-step explanation:
21-3/4=20.25
a+b=21
a=21-b
b=3/4*a
b=3/4*(21-b)
b=3(21-b)/4
b=63-3b/4
4*b=63-3b
4b+3b=63
7b=63
b=63/7
b=9
