If we draw one digonal for given parallelogram , then it will divide the parellelogram in two equal triangles (since the opposite sides of parallelogram are equal).

and formula for area of triangle if two sides and angle between them is given = (ab sin C)/2

Here in the question , a=8,b=10 and angle C = 60

so, area of 1 triangle = (8*10*sin 60)/2 = 40 sin 60

but sin 60 = sqrt(3) /2

so, area of 1 triangle = (40*sqrt(3))/2 = 20*sqrt(3)

therefore area of parallelogram = 2*area of 1 triangle = 2*20*sqrt(3) = 40 sqrt(3)

If we have to write it in decimal notation , then sqrt(3) = 1.732(approx)

therefore, area of parallelogram = 40*1.732 = 69.28 (approx)

Hence, area of parallelogram = 40*sqrt(3) = 69.28 (approx.)

Msg me if you have any further doubt :)