Cody is saving money for a new skateboard that costs $77.99. he already has $20 in his savings account. he earns $6 for every lawn he mows. if he mows 3 lawns a weekend, how long will it take him to save enough money for the skate oard?

Cost of the skateboard = $77.99

Amount that he already has = $20

 $77.99 - $20 = $57.99
He still needs $57.99

He earns $6 for every lawn he mows.

$57.99  ÷ 6 =  9.65
He needs to move 10 lawns to earn that $57.99.

He can mow 3 lawns a weekend.

10 ÷ 3 = 3 1/3 
He needs to work on 4 weekends to mow the 10 lawns.

It will take him 4 weekends to save enough to buy the skateboard.