in a school 4upon7 of the students are boys if there are 210 girls find the number of boys in the school

Can some one me with these questions

Julia bought 7 hats a week later half of all her hats were destroyed in a fire. there are now only 12 hats left with how many did she start

A0.40 kg soccer ball is kicked so that its incoming velocity of 5 m/s is changed to an outgoing velocity of -25 m/s. what impulse does the player apply to the ball?