PLS HELP IM BEGGING MULTIPLE CHOICE

Sum of brother and sisters age is 26. four times the brothers age is subtracted from three times the sisters age, the difference is 8. what are the ages of the brother and sister?

If 22.5 of nitrogen at 748 mm hg are compressed to 725 mm hg at constant temperature. what is the new volume?

Why is it incorrect to balance a chemical equation by changing the subscripts? explain.