When Jennifer does 9 push-ups and 6 sit-ups. it takes a total of 45 seconds. In comparison, she needs 69 seconds to do 9 push-ups and 14 sit-ups. How long goes it take Jennifer to do
each kind of exercise

21.4 i did it already for s1

step-by-step explanation:

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.