Răspuns :
notam cu C ciresele de la inceput.
Avem (C+3)*3+51 =900
C+3 = (900-51)/3
C+3 = 283
C= 280
(a+3)×3+51=900
(a+3)×3=900-51
(a+3)=849:3
a+3=283
a=283-3
a=280
verificare:(280+3)×3+51=900
(a+3)×3=900-51
(a+3)=849:3
a+3=283
a=283-3
a=280
verificare:(280+3)×3+51=900