X< -4
You need to do inverse operations and add 12 to both sides.
By proportionality, for any number

, if T is multiplied by

then the same goes for M.
a) M has been multiplied by

hence


b) T has been divided by

hence

The sale price was 30% off the original price, which means it was on sale for 70% of the original cost ( 100% - 30% = 70%)
To find the original cost, divide the sale price by the percent of the original cost:
21 / 0.70 = 30
The original price was $30
check:
30 x 0.3 = 9 ( amount of discount)
30 - 9 = 21 ( sale price)