Question 747848
If you draw the picture, you will see that it is a right triangle you are solving for. To solve for the hypotenuse(the ladder in this case) you would use the Pythagorean theorem which is {{{ a^2+b^2=c^2 }}}. When you substitute in your values you get {{{ 18^2+6^2=c^2 }}}
Next simplify and get {{{ 324+36=c^2 }}}.  Simplify some more and now you have {{{ 360=c^2 }}} Square root both sides and do some rounding to get that the ladder is approximately 19 feet long.