Let the larger number be 'x' and smaller number be 'y'.
Since, the sum of two numbers is 21.
So, [tex] x+y=21 [/tex] (equation 1)
Since, the larger number is six less than twice the smaller number.
So, [tex] x=2y-6 [/tex] (equation 2)
Substituting the value of 'y' from equation 2 in equation 1.
So, [tex] x+y=21 [/tex]
[tex] 2y-6+y=21 [/tex]
[tex] 3y = 27 [/tex]
So, y=9.
Since, x+y=21
x = 21-y
x = 21-9
x = 12.
So, the larger number is 12 and smaller number is 9.