"Dad, where had you been?" asked Jack.
"I had been to the attic, my son," replied Dad. "And do you know what I saw there? There was a big web with 20 spiders and flies on it?"
"How many spiders were there?" asked the little boy with curiosity.
"Well, there were a total of 130 legs on the web," answered Dad with a smile.
"Now you can find out how many spiders were there?"
Can you help the little boy find out how many spiders were on the web in the attic?