The length ratio of the waist to the ground side of an isosceles triangle is 4:3. Its circumference is 77cm. What is the length of the ground side?

The length ratio of the waist to the ground side of an isosceles triangle is 4:3. Its circumference is 77cm. What is the length of the ground side?

Solution 4 + 4 + 3 = 11
The bottom edge is 77 × 3 / 11 = 21 cm