**Complete the equations to prove that vertical angles always have equal measure.**  ||| - | -: | - $\text{In terms of } \green b \text{ and a number} \\\text{in degrees,}$ | $\purple c=$ | [[☃ expression 2]] $\text{In terms of } \green b \text{ and a number} \\\text{in degrees,}$ | $\pink a=$ | [[☃ expression 4]] | $\text{Combining these equations to } \\ \text{get } \pink a \text{ in terms of } \purple c,$ | $\pink a=$ | [[☃ expression 5]]