Question 827102
base:leg is 5:6.


Trying to draw a picture could help.  Triangle, two legs equal, the "base" length a little shorter than the leg length (I assume you only mean either leg, not both legs combined).


The factor of the parts of the units of the sides to the perimeter is unknown.  Five and six of what would give 85 cm?  We need a factor, call it x.


{{{highlight_green(5x+6x+6x=85)}}}, perimeter equation, not yet knowing actual size of the sides; only knowing ratio among the sides.  You need to be sure you understand all this before you can continue.  IF you DO understand, then you can finish the rest of the problem.  If you do not yet understand, then you need that help, first.