Solve 7x + 8 = 78

The solution of 7x + 8 = 78 is x = 10.

7x + 8 = 78\ \Rightarrow\ x = 10

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The lines y = 7x + 8 and y = 78 meet at x = 10. The solution of the equation is the x-coordinate of the point where the two sides are equal.

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.
$7x + 8 = 78$
2
Subtract 8 from both sides:
$7x + 8 - 8 = 78 - 8 \ \Rightarrow\ 7x = 70$
3
Divide both sides by 7:
$\frac{7x}{7} = \frac{70}{7} \ \Rightarrow\ x = 10$
4
Check: put x = 10 back into the equation.
$7\cdot10 + 8 = 70 + 8 = 78 \checkmark$

LaTeX source of the formulas on this page

\[ 7x + 8 = 78\ \Rightarrow\ x = 10 \]
\[ 7x + 8 = 78 \]
\[ 7x + 8 - 8 = 78 - 8 \ \Rightarrow\ 7x = 70 \]
\[ \frac{7x}{7} = \frac{70}{7} \ \Rightarrow\ x = 10 \]
\[ 7\cdot10 + 8 = 70 + 8 = 78 \checkmark \]

Trying values of x in 7x + 8 = 78

x	7x + 8	Equals 78?
8	64	no
9	71	no
10	78	yes
11	85	no
12	92	no

Questions

What is x in 7x + 8 = 78?

The solution of 7x + 8 = 78 is x = 10.

How do you solve 7x + 8 = 78?

Subtract 8 from both sides to get 7x = 70, then divide both sides by 7 to get x = 10.

How do I check the answer?

Replace x by 10: 7(10) + 8 = 78, which is 78.

Solve 7x + 8 = 78

How to work it out

Trying values of x in 7x + 8 = 78

Questions

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