The expression is “seven times a number equals -18”.

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Let n represent the number.

The word “equals” can be represented as “=” symbol.

The word “times” indicates multiplication and the symbol is “”.

Rewrite the sentence into expression as \ \

Rewrite the sentence into expression as 

According to division property of equality:

For any number a, b and c, If a = b then

                 (Divide each side by 7)

                     (Cancel common factors)

The number is .