You walk 10 miles north, 20 miles south, and 5 miles north. taking north to be the positive y direction, define a position vector that describes your position on the y-axis.

Considering north as positive Y axis

       First  10 miles north means a positive 10 displacement along y direction

      Second 20 miles south means a negative 20 displacement along y direction

       Third 5 miles south means a positive 5 displacement along y direction

So total displacement = 10 - 20 + 5 = -5 miles displacement

So position vector of the final position = - 5 j

  the grams     of oxygen gas   that can be produced     is 20.6   grams of o₂

calculation

2liclo₃ →   2 licl + 3 o₂

step 1:   find the moles of liclo₃

moles = mass÷ molar mass

from periodic table the molar mass of liclo₃ =6.9 +35.5   +(16 x3) =90.4 g/mol

moles=38.7 g÷90.4 g/mol=0.4281   moles

step 2:   use the   mole ratio   to calculate the moles of o2

from equation above, liclo₃: o₂   is 2: 3  

therefore the moles of   o₂=0.4281 moles x3/2 =0.6422   moles

step 3: find mass   of o₂

mass= moles x molar mass

from periodic table the   molar mass of   o₂ = 16 x2= 32 g/mol

mass=0.6422   moles   x   32 g/mol = 20.6 grams of o₂