Substitute x for "a number". This is a verbal equation, so it will look like this:
3x+4x+1=6x. Then solve for x.
So we multiply both sides by 7 to make 2/7 a whole number. You get 2(4q+7/2)-21q=63. Then take 4q+7/2 out of parentheses and you get 8q+7-21q=63. Subtract 7 on both sides and add the q’s together, -13q=56. Divide both sides by -13 and you get around 4.3

-8400/68 simplifies to to -2100/17, dolphins/year, so 2100 less dolphins every 17 years.
and we can just divide those to get the decimal amount of -123.53, which means, 123.53 less dolphins every year.
of course, there's no such a thing as 0.53 of a dolphin, so, we can say "about" 123 less dolphins per year.


➼ 
➼ 
➼ 
➼ 
Therefore, the value of n is 30.


✒ 
✒ 
✒ 
Hence verified.
