Question

What is this 15=2+4-d

Answer 1

15=2+4-d

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