First we look at the this underlined part:

    "the sum of a number y and 8" means "add y and 8", so that's
     y+8, so we put it in parentheses, (y+8), and replace those
     underlined words by (y+8): 

Next we underline this part:

    "the quotient of 50 and (y+8)" means "divide 50 by (y+8)",
     so we put 50 over (y+8), like this,  so we 
     put it in parentheses, , and replace those
     underlined words by :

Now we just underline:

And of course "twice" means "2 times":

So we end up with 

 or



Edwin