10 × { 10 + 10 × [ 0, 3 + 0, 3 × ( 3, 3 - a ) ] } = 220
10 + 10 × [ 0, 3 + 0, 3 × ( 3, 3 - a ) ] = 220 : 10
10 + 10 × [ 0, 3 + 0, 3 × ( 3, 3 - a ) ] = 22
10 × [ 0, 3 + 0, 3 × ( 3, 3 - a ) ] = 22 - 10
10 × [ 0, 3 + 0, 3 × ( 3, 3 - a ) ] = 12
0, 3 + 0, 3 × ( 3, 3 - a ) = 12 : 10
0, 3 + 0, 3 × ( 3, 3 - a ) = 1, 2
0, 3 × ( 3, 3 - a ) = 1, 2 - 0, 3
0, 3 × ( 3, 3 - a ) = 0, 9
3, 3 - a = 0, 9 : 0, 3
3, 3 - a = 3
a = 3, 3 - 3
a = 0, 3