1) A committee consisting of 3 girls and 4 boys can be formed in 1C3×9C4 ways
2) Since, the committee requires 7 members and it must have at least 3 girls means the committee can consist 3 or more number of girls.
This can be done in two ways, i.e., select 3 girls from 4 or all the 4 girls.
By the principles of combination, we can select 4 boys from 9 and 3 girls from the 4 or also 3 boys and 4 girls.
This can be computed as total (9C4 * 4C3) + (9C3 * 4C4) ways