This question requires a bit of understanding on what it’s asking for.
(a) When the equations have no solution, it means that there are no intersections. Given that both of these equations are straight lines, it means that you’re trying to find a value of a such that both lines are parallel.
Rewriting the equations into y = mx + c:
Equation 1: y = 3 x + 5
Equation 2: 5y = a x + b
y = a/5 x + b/5
By matching up the gradient, a/5 = 3. a = 15.
(b) When the equations have infinite solutions, it means that they are the same line.
Hence, a is actually also 15, whereas is you compare the y-intercept of both equations, you can equate b/5 = 5. Thus, b = 25