We are given:
The number of blocks Tegan still needs to make = m.
The number of blocks Tegan has completed = c.
Total number of more snow blocks need to make = 68 .
Total number of more snow blocks need to make = Total number of blocks - The number of blocks Tegan has completed.
m = 68 - c.
Therefore, the equation for the number of blocks Tegan still needs to make, m, when she has completed c blocks is
