Evaluate 5y + 4x    when y=10 and x= -5 

5y+4x

5(10) + 4(-5)

50 - 20

30

Well, the equation would become 5*10 + 4*-5. (because when a number and a variable are right next to each other, that means they are multiplying). Now all you have to do is solve using the Order of Operations.
5*10+4*-5
50+ 4*-5
50-20
30
You are left with 30 as the correct answer. Hope this helped!