A pressure difference gives a checked one-dimensional net force. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A pressure difference is checked first
Left pressure 8 pascals minus right 2 pascals gives difference 6 pascals.
8minus2=6
The difference times area gives the net push
Difference 6 pascals over area 3 square metres gives net force 18 newtons to the right.