A restaurant sells a coffee refill mug for $6. Each refill costs $2. Last month Keith spent $30 on a mug and refills. Write an equation
you can use to find the number of refills Keith bought. Use x for
your variable and do NOT type and spaces. *

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.