How do I work 2s^3-4r^2 if s=5 and r=1?

Answer 1

I would assume you just replace all the r's with 1, and all the s's with 5:

2(5^3)-4(1^2)
= 2(125)-4(1)
= 250-4
= 251

Just plug and chug. I assume the arithmetic does not cause problems...

Answer 2

that is what I thought thank you!