Răspuns :
a x 9 - ( 13 x 4 ) = 57
a x 9 - 52 = 57
a x 9 = 57 + 52
a x 9 = 109
a = 109 : 9
a = 12 , (1)
a x 9 - 52 = 57
a x 9 = 57 + 52
a x 9 = 109
a = 109 : 9
a = 12 , (1)