I think Its 6.............
I redrew the triangle (just turned it around it make it easier to understand).
September
30-10=20 days
October 31
November 10
Time=20+31+10=61 days
A=42,000×(1+0.035÷365)^(61)
A=42,246.38
Interest earned
I=42,246.38−42,000
I=246.38
21*x=9*21
9*21=189
21*x=189
Divide 189 by 21 to solve for X or in this case "Blank"
189/21= 9
All in all you would get the answer x+y=1.