This is a typical story problem that needs to be translated from written words to a workable equation. "An angle measures" looks like "A =" in equation form. "...the measure of a supplementary angle" looks like "(180 - A)" and "143.4 more" means you're adding 143.4 to the (180 - A). So in the end the equation is this: A = (180 - A) + 143.4. This simplifies to A = 323.4 - A, and adding A to both sides gives us 2A = 323.4 and A = 161.7. Now check yourself by filling in 161.7 for every A in your original equation and make sure it comes out right and that the right side does in fact equal the left side. (It does, just check it anyway!)