The missing number in the given sequence 343, 1331, _______, 4913 is

It takes two hours for a person X to mow the lawn. Y can mow the same lawn in four hours. How long (in minutes) will it take X and Y, if they work together to mow the lawn?

Functions F(a, b) and G(a, b) are defined as follows:
F(a, b) = (a - b)² and G(a, b) = |a - b| , where |x| represents the absolute value of x.
What would be the value of G(F(1, 3), G(1, 3))?

For what values of k given below is $${{{{\left( {k + 2} \right)}^2}} \over {k - 3}}$$ an integer?