Use the figure below for #15 - 16. PQ = 4x - 5, QR = 6x + 25, PR = 100. I don’t know how my teacher got 5 for x. I just want to see the step-by-step answer because I want to study for the test. Thank you in advance.

Data from 2005 for various age groups show that for each $100 increase in the median weekly income for whites, the median weekly income of blacks increases by $105. also, for workers of ages 25 to 54 the median weekly income for whites was $676 and for blacks was $527. (a) let w represent the median weekly income for whites and b the median weekly income for blacks, and write the equation of the line that gives b as a linear function of w. b = (b) when the median weekly income for whites is $760, what does the equation in (a) predict for the median weekly income for blacks?