What are the eight-digit grid coordinates for spot elevation 85?

Pick the expression that matches this description: a polynomial of the 5th degree with a leading coefficient of 7 and a constant term of 6 (choice a) 7x^5+2x^2+6 (choice b) 7x^6−6x^4+5 (choice c) 6x^7−x^5+5 (choice d) 6x^5+x^4+7

Guys i really need or i have to stay late up night

Can someone check if i did this correct. it’s number 4 if you’re wondering.