Given data,
Mary earns $12 per/ hr + 10% commission on all her sales.
Mary worked $10 hr
Her sales were $1500
Then,
Mary earns $12*10 = $120 ( working 10 hr)
She got commission 10 % on her sales of $1500
That is, 10% * 1500
= (10/100)* 1500
= $150
Therefore,
Her total earning is = $150 + $120
= $270