Help on algebra 1 problems?

hey, i'm in algebra 1 and my teacher gave me this worksheet to fill out. i'm having problems on these 2..."the total value of the $5 bills and $10 bills in cash is $410. there are eight more $10 bills than $5 bills. how many of each are there?" and "rockjaw spends a total of $80 each week for karate lessons and ballet lessons. if the amount spent on karate lessons increases $10 per we ek, it will be twice the amound spend on ballet lessons. How much does he spend on ballet lessons?" please help! =) thanks