A sample of radium has a weight of 2.5 mg and a half-life of approximately 8 years.
a. How much of the sample will remain after 8 years? 4 years? 2 years?
b. Find a function which models the amount of radium f(t), in mg, remaining
after t years.

Where m is the slope of the line and b is the y-intercept of the line, or the y-coordinate of the point at which the line crosses the y-axis. to write an equation in slope-intercept form, given a graph of that equation, pick two points on the line and use them to find the slope. this is the value of m in the equation.