Initial amount = d dollars
Amount spent = $12
Because the amount left is at least $51, therefore
d - 12 ≥ 51
Add 12 to each side.
d ≥ 51 + 12
d ≥ 63
Note: The amount left is at least $51. Therefore the amount left should be $51, or greater than $51.
Answer:
d - 12 ≥ 51
d ≥ 63