A=c + (-10) Solve for c in terms of other variables.

To do this we need to move 10 to other side. To accomplish this you just need to add 10 to both side since (-10)

so

A + 10 = c - 10 + 10

we get

A + 10 = c

lets say it wasn't - 10 but positive 10.

A = c + 10 then we would subtract 10 from both sides

A - 10 = c + 10 - 10

we get

A - 10 = C