SAT Algebra practice question

In the xy-plane, the graph of the equation ax - 6y = 24, where a is a constant, has an x-intercept of (d, 0) and a y-intercept of (0, d - 10). The system of equations consisting of ax - 6y = 24 and 6x - by = c, where b and c are constants, has infinitely many solutions. What is the value of c?