#### Answer

b=3

#### Work Step by Step

In order to solve this algebraic expression, we must isolate the variable. A variable is the letter in the problem (for instance, in the equation x+2=10, x is the variable). Because addition and subtraction are inverse operations (they cancel each other out), we know we must add when a number is being subtracted from the variable and subtract when a number is being added to the variable.
In the equation b+4=7, we must get rid of the 4, which is on the same side as b, in order to solve. Thus, we subtract 4 on both sides of the equation to find that b=3. We plug 3 in for b and confirm that our answer is, indeed, correct.