How do i find an equation for a line with an x-intercept of 4 and a y-intercept of -2

The equation of a line is y = ax + b, where a is the slope and b is the y-intercept.  

Since we have the y-intercept, all we need to do is find the slope. To find the slope, you need 2 coordinates.

The y-intercept is where the line crosses the y axis, so it is where x is 0. Since the y intercept is -2, that means the first coordinate is (0, -2)

The x-intercept is where the line crosses the x axis, so it is where y is 0. Since the x intercept is 4, that means the second coordinate is (4, 0)

Since we already have the y-intercept, all we do is put the slope in the equation: y = 1/2x - 2.

Step-by-step explanation:

you didn't post any answer choices, so its not 100% clear what your teacher is looking for

however, log(15/7) is equivalent to log(15) - log(7)

i'm using the rule log(x/y) = log(x) - log(y)