$\overleftrightarrow{JK}$ and $\overleftrightarrow{LM}$ are parallel lines. The interior angles of a triangle sum to $180^\circ$. **Complete the equations to prove that alternate interior angles always have equal measure.**  ||| - | -: | - $\text{In terms of } \purple c \text{ and a number} \\\text{in degrees,}$ | $\green b=$ | [[☃ expression 2]] $\text{In terms of } \purple c \text{ and a number} \\\text{in degrees,}$ | $\pink a=$ | [[☃ expression 3]] | $\text{Combining these equations to } \\ \text{get } \pink a \text{ in terms of } \green b,$ | $\pink a=$ | [[☃ expression 4]]