An object is moving with velocity `10 ms^(-1)`. A constant force acts for `4 s` on the object and gives it a speed of `2 ms^(-1)` in opposite direction. The acceleration produced is
Options:
(a) `3ms^(-2)`
(b) `-3 ms^(-2)`
(c) `6 ms^(-2)`
(d) `-6 ms^(-2)`