1 + [ 2 × ( 1 + c ) - 59 ] × 9 = 10
[ 2 × ( 1 + c ) - 59 ] × 9 = 10 - 1
[ 2 × ( 1 + c ) - 59 ] × 9 = 9
[ 2 × ( 1 + c ) - 59 ] = 9 : 9
[ 2 × ( 1 + c ) - 59 ] = 1
[ 2 × ( 1 + c ) ] = 1 + 59
[ 2 × ( 1 + c ) ] = 60
1 + c = 60 : 2
1 + c = 30
c = 30 - 1
c = 29
