Ratkaise kuvion "sääntö". Kirjoita puuttuva luku.

a.
[[$\qquad$]] 84 [[$\,\,\,\,\,\,\,\,\,$]] 55 [[$\quad \, \, \, \,$]] 31 [[$\quad \,\,\,$]] 11
[[$\qquad \, \, \, \, \, \, \, \, \, $]] 29 [[$\,\,\,\,\,\,\,\,\,$]] 24 [[$\quad \, \, \, $]] 20
[[$\qquad \quad \quad\,\,\,\,\,\,\,\,\,$]] 5 [[$\,\,\,\,\,\,\,\,\,$]] 4
[[$\qquad \qquad \quad \, \,\,\,\, $]]

b.
[[$\qquad$]] 15 [[$\,\,\,\,\,\,\,\,\,$]] 14 [[$\quad \, \, \, \,$]] 13 [[$\quad \,\,\,$]] 12
[[$\qquad \, \, \, \, \, \, \, \, \, $]] 29 [[$\,\,\,\,\,\,\,\,\,$]] 27 [[$\quad \, \, \, $]] 25
[[$\qquad \quad \quad\,\,\,\,\,\,\,\,\,$]] 2 [[$\,\,\,\,\,\,\,\,\,$]] 2
[[$\qquad \qquad \quad \, \,\,\,\, $]]