Can somebody explain to me how the acceleration in simple hormonic motion is proportional to the displacement..

When you graph simple harmonic motion in an acceleration versus displacement graph, the graph at any point would be linear. The graph would also pass through the origin giving proportionality of acceleration to negative displacement. Definition of proportionality neglects the negative value of the displacement so therefore acceleration is proportional to displacement. The acceleration of the motion is always directed towards equilibrium and so at maximum displacement, there would be greatest negative acceleration and vise versa.At the origin, the displacement would be zero and acceleration would also be zero

Divide 108.2 x 10^6 into 1.5 x 10 and the result will be in au (astronomical units)

Make them both to where they have the denominator of 18that makes 3/2 equal 27/18 and 1/9 equal 2/18so now you have  27/18x+5=2/18subtract 5 from the other sideso now you have 27/18x+2/18-5then subtract 2/18 from 27/18 to get 25/18x=-5then divide 25/18 by -5 and your answer will be  -5/18