Let x be the unknown number: "10 less than six times the same number" becomes: "15 more than four times the mystery number" becomes: Perimeter is the sum of the sides, so if you put these expressions together, you get: Subtract 10 from both sides to isolate the variable: Go back to each expression and replace x with 9 km: To confirm our sides, add to see if they equal the given perimeter: Well done! It depends on where the angle is situated in relation to the two sides. The height is not needed. But what happens when you have a combined figure, a shape that is the combination of several simpler shapes? I need to describe a triangle minimal perimeter using this information. The simplest two-dimensional shape is the triangle, and an equilateral triangle has three congruent sides. Jay Willis. You used algebra to solve a perimeter problem! Perimeter of triangle: len of hypotenuse + len of base + len of height. I then add all three sides. How to find perimeter of a triangle - SSAT Middle Level Math. Finding the Perimeter When Three Side Lengths are Known, {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/3\/38\/Find-the-Perimeter-of-a-Triangle-Step-1-Version-2.jpg\/v4-460px-Find-the-Perimeter-of-a-Triangle-Step-1-Version-2.jpg","bigUrl":"\/images\/thumb\/3\/38\/Find-the-Perimeter-of-a-Triangle-Step-1-Version-2.jpg\/aid2157327-v4-728px-Find-the-Perimeter-of-a-Triangle-Step-1-Version-2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":728,"bigHeight":546,"licensing":"