With this information I am to find the linear equation: f(−5)=−4 and f(5)=2The solution is...

With this information I am to find the linear equation: f(−5)=−4 and f(5)=2
The solution is provided as $y=\frac{3}{5}x-1$ however I arrived at $y=\frac{7}{10}x-\frac{3}{2}$
Here is my working:
Using these points, find the equation: (-5,-4)(5, 2)
the slope m: $m=\frac{y1-y}{x1-x}$=$\frac{2+5}{5+5}$=$\frac{7}{10}$
Now that I have m, plug the values of one of the pairs into the linear function form to find b: $y=mx+b$
$2=\frac{7}{10}(5)+b$
$\frac{7}{10}(5)+b=2$
$\frac{7}{2}+b=2$ #7/10 * 5 = 7/2
$b=2-\frac{7}{2}$
$b=-\frac{3}{2}$
$y=\frac{7}{10}x+\frac{3}{2}$
Where did I go wrong and how can I arrive at $y=\frac{3}{5}x-1$?