What is the value if s in the equations 3r = 10 +5s , when r=10
a. 4
b. 8
c. 100
d. 200

Your answer is 4,

You take r which is 10 and plug it in the equation, which is 3(10)=10+5s.
Multiply, 30=10+5s.

Now we cross over our like terms, 10 to 30. (TIP; if a number crosses the equal sign it changes signs).

So, now we subtract; 30-10=5s

Which gives us 20=5s.

All that's left is to divide 20 by 5.
20/5 = 4