Write an expression for " 9 less than three times a number"

3x - 9

Step-by-step explanation: "9 less than three times a number" does not mean 9 minus three times a number, less than actually switches the order around so that 9 less than three times a number actually means three times a number minus 1 which can be read as 3x - 9.

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.