,, a" - numarul bilelor din cutie
[ ( a + 30 ) × 5 - 200 ] : 20 = 20=>( a + 30 ) × 5 - 200 = 20 × 20=>
( a + 30 ) × 5 - 200 = 400=>( a + 30 ) × 5 = 400 + 200
=>( a + 30 ) × 5 = 600
a + 30 = 600 : 5
a + 30 = 120
a = 120 - 30
a = 90 bile are Darius in cutie