What, exactly, is your question? How can you look at this problem and immediately know the answer, without doing any calculation at all? Can't help you there because I certain couldn't do that! I do know of several different ways to do this problem but I don't know which is appropriate for you because I don't know what "tools" you have available! The simplest would be if you know the formula: if an object has initial speed v at angle with the horizontal, they the distance it goes in time t is and the height in that same time is where "g" is the acceleration due to gravity: 32.2 feet per second per second.
The distance the javelin will travel is the x value when y is again 0.
For (C) do the same using 45 degrees instead of 40 degrees.
For (B) do the calculation with the variable " " still in it. Set the x distance, when y= 0, equal to 280 and solve for .