David ate 2 1/7 pizzas and gave 1 3/14 pizzas to his mother. How many pizzas did David have initially? i really need help asap

Which expression is equivalent to? assume x > 0 and y > 0.

Ascientist wants to use a model to present the results of his detailed scientific investigation. why would a model be useful? a )because the model makes the concepts easier to understand b) because the model is easy to put together and to use c) because the model prevents other scientists from asking questions d) because the model requires the audience to pay full attention to it i don't know what to choose because between a and d a is much more likely than d because it only wants to get the attention of the audience. i'm confuse.

3x = 729 solve for x plz . it's urgent. will mark