Can someone explain how to solve this problem fast!

Subtract 4 to both sides:



Factor:

We want to find out what two numbers will multiply to get and add up to get . Our quadratic is in the form of . So in this case, a is 6, b is -5, and c is -4. . And we know that b is -5, so we want to find two numbers that will multiply to get -24 and add up to get -5. These two numbers are 3 and -8. Rewrite -5b in the quadratic with these:



Now factor them separately:



As you can see (2b + 1) is common for both terms, so we can just group the beginning of the terms together to get:



Set each one equal to 0 and solve for 'b':



Add 4 to both sides:



Divide 3 to both sides:





Subtract 1 to both sides:



Divide 2 to both sides:

The answer to that is 6