Stocks A, B and C are priced at rupees 120, 90 and 150 per share, respectively. A trader holds a portfolio consisting of 10 shares of stock A, and 20 shares of stocks B and C put together. If the total value of her portfolio is rupees 3300, then the number of shares of stock B that she holds, is

Let the number of stocks B hold be $$x$$

So, number of stocks C hold is $$20-x$$

So, $$10\times\ 120+90\times\ x+150\times\ \left(20-x\right)=3300$$

or, $$1200+90\ x+150\left(20-x\right)=3300$$

or, $$1200+90\ x+3000-150x=3300$$

or, $$4200-60x=3300$$

or, $$60x=900$$

or, $$x=\dfrac{900}{60}=15$$

So, the number of shares of stock that B hold is 15.