X² + y² - 4 x + 2 y = b
x² - 4 x + 4 + y² + 2 y + 1 = b + 4 + 1
( x - 2 )² + ( y + 1 )² = b + 5
y - coordinate of the center of the circle is: y = - 1
b + 5 = r
b + 5 = 7
b = 7 - 5
b = 2
It would be a mixed number 14 4/10, which can be simplified to 14 2/5.