Which expression is equivalent to −10+(−40)+(−90) ?
d.−10+(−90)+(−40)
s. −10−(40−90)
b. −(10−40)+(−90)
c. 10+40+90

It is easy, answer D.

If you see, on answer D commutative property is applied.

-10 - 40 - 90 = -140

-10 - 90 - 40 = -140

It is always -140

It can't be S because -10 - (40-90) = -10 - (-50) = -10 + 50 = 40

It can't be B because -(10-40) - 90 = - (-30) - 90 = + 30 - 90 = - 60

It can't be C because it would give +140

So, answer D is right.