x = 10
Here's how I got my answer:
Step 1: Add x to both sides, which leaves us with [tex] -1 = x - 21 + x [/tex]
Step 2: Simplify [tex] x - 21 + x [/tex] to [tex] 2x - 21 [/tex], which leaves us with [tex] -1 = 2x - 21 [/tex]
Step 3: Add 21 to both sides, which leaves us with [tex] -1 + 21 = 2x [/tex]
Step 4: Simplify [tex] -1 + 21 [/tex] to 20, which leaves is with [tex] 20 = 2x [/tex]
Step 5: Divide by sides by 2, leaving us with our answer, x = 10
