First, you distribute 0.8 through the parentheses by multiplying 0.8 by s and -12, which gets you to 0.8s-9.6. Now, the equation is changed to 0.3s+0.8s-9.6=33.3. Then, you add like terms (add the two numbers with the s) by doing 0.3s+0.8s which gets you to 1.1s-9.6=33.3, all thats left is adding 9.6 on both sides which gets you to 1.1s=42.9. Now finally, you divide 42.9 by 1.1 and you get 39. The value of s in the equation is 39.