Answer:
-9
Step-by-step explanation:
15=2+4-d
15+d=6
d=-9
15=6-d
Move 6 to the other side
Sign changes from +6 to -6.
15-6=6-6-d
15-6=-d
9=-d
Multiply both sides by -1 to get +d
(9)(-1)=(-d)(-1)
Answer: d=-9
