Solve 3x + 7 = 28
The solution of 3x + 7 = 28 is x = 7.
How to work it out
- 1
The goal is to get x alone. Undo the operations in the opposite order: first the addition, then the multiplication.
- 2
Subtract 7 from both sides:
- 3
Divide both sides by 3:
- 4
Check: put x = 7 back into the equation.
LaTeX source of the formulas on this page
\[ 3x + 7 = 28\ \Rightarrow\ x = 7 \]
\[ 3x + 7 = 28 \]
\[ 3x + 7 - 7 = 28 - 7 \ \Rightarrow\ 3x = 21 \]
\[ \frac{3x}{3} = \frac{21}{3} \ \Rightarrow\ x = 7 \]
\[ 3\cdot7 + 7 = 21 + 7 = 28 \checkmark \]Trying values of x in 3x + 7 = 28
| x | 3x + 7 | Equals 28? |
|---|---|---|
| 5 | 22 | no |
| 6 | 25 | no |
| 7 | 28 | yes |
| 8 | 31 | no |
| 9 | 34 | no |
Questions
What is x in 3x + 7 = 28?
The solution of 3x + 7 = 28 is x = 7.
How do you solve 3x + 7 = 28?
Subtract 7 from both sides to get 3x = 21, then divide both sides by 3 to get x = 7.
How do I check the answer?
Replace x by 7: 3(7) + 7 = 28, which is 28.