Set up equations based on the properties of an equilateral triangle.

:
For Fig. 7.1, it is assumed that the third side is $(a+b+2)$ cm, interpreting 'c' as '2' to allow for numerical solutions.

Step 1: Set up equations based on the properties of an equilateral triangle.
In an equilateral triangle, all sides are equal.

$$4a = 3b \quad (1)$$ $$4a = a+b+2 \quad (2)$$

Step 2: Solve the system of equations for $a$ and $b$.
From equation (2):

$$4a - a = b+2$$ $$3a = b+2$$ $$b = 3a-2 \quad (3)$$

Substitute equation (3) into equation (1):

$$$$