(2,-1) y-intercept -3 slope 1/2 write an equation with the given info above.

y-intercept -3  

slope 1/2

is sufficient info with which to write an equation for a straight line:

y = mx + b becomes y = (1/2)x - 3.

You should check this by determining whether or not (2,-1) satisfies this equation.

Each day he walks them 1/3 of an hour in the morning and 1/2 an hour in the afternoon.
We can add these together to find out how long they are walked each day.
1/3 + 1/2 =
The lowest common multiple of 3 and 2 is 6, therefore we turn the denominators into 6
From 3 to 6, we multiply by 2, therefore we do the same to the numerator
1/3 = 2/6
From 2 to 6, we multiply by 3, therefore we do the same to the numerator
1/2 = 3/6
Now we can add the numerators
2/6 + 3/6 = 5/6

Carl only walks them for 5/6 of an hour, therefore we multiply this by $3.25 to work out how much he earns a day
5/6 x $3.25 = $2.7083
If we round to the nearest penny, he earns $2.71 per day 

If he walked the dog every day in the week, then we need to multiply what he earns each day by 7 to get a weekly earning
$2.71 x 7 = $18.97 per week