Question $9$:

Ten years ago, Sarah and Ben bought a house in Cambridge, Ontario for $$600,000.$ They made a down payment of $$50,000$ and took out a mortgage to cover the remaining $$550,000.$ They have now paid $$100,000$ towards the mortgage principal. How much equity do they have in their home?

a$.$ $$50,000$

b$.$ $$150,000$

c$.$ $$550,000$

d$.$ $$450,000$