Răspuns:
( a × 3 - 10 ) : 5 + ( 6 × 15 ) = 100
( a × 3 - 10 ) : 5 + 90 = 100
( a × 3 - 10 ) : 5 = 100 - 90
( a × 3 - 10 ) : 5 = 10
a × 3 - 10 = 10 × 5
a × 3 - 10 = 50
a × 3 = 50 + 10
a × 3 = 60
a = 60 : 3
a = 20
verificare
( 20 × 3 - 10 ) : 5 +( 6×15 ) = 100
( 60 - 10 ) : 5 + 90 =
50 : 5 + 90 =
10 + 90 = 100