Question 29767
Hi,

Lets call {{{y}}} the number of years past 1987, so if {{{y=3}}} we would be talking about 1990.

The number of millions of dogs in any given year is {{{34.7-0.025y}}} because in 1987 there were 34.7 million dogs, and for every year after that, the number of dogs decreases by 0.025 million.

We can form a similar expression for the cats. Number of million cats is {{{27.7+0.375y}}} That's because in 1987 we start with 27.7 and for every year after that ownership increases by 0.375.

So what we need to know is when the number of cats equals the number of dogs. This  happens when {{{34.7-0.025y=27.7+0.375y}}}. Hopegully you can solve this to get the answer of 17.5 years. If not write back and we can go through solving the equation.

Hope that helps,
Kev