Figuring out yards of crush

Hi All,

Planning on a rink in the backyard this summer and have checked the high and low points, going to need to bring in some crush to bring a section of the yard up on the low corner. here are some numners, having a heck of a time figuring out how many yards of crush to order.

Rink Size 50 x 35

I have attached a picture of my awesome drawing skills so you can see the drops and numbers.

The high posts on the back are level horizontally, the starting high post is marked at 4 inches as that is roughly how much ice I want. I need to bring the rest of the area up to same level. Keeping in mind I want to save 2 inches for topsoil in the spring as we will be planting clover.

If it was same depth over whole area I wouldn't have a problem but this one has me banging my head!