Considering boys row, left-handed boys + right-handed boys must be equal to 35, then:
17 + right-handed boys = 35
right-handed boys = 35 - 17
right-handed boys = 18
Considering left-handed column, left-handed boys + left-handed girls must be equal to 29, then:
17 + left-handed girls = 29
left-handed girls = 29 - 17
left-handed girls = 12
