First you had to remove parenthesis first.

Multiply by the numbers.

Final answer 



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-Charlie
Answer:
In step 2, the subtraction property of equality was applied
In step 4, the division property of equality was applied
Step-by-step explanation:
Perimeter = 4 x sides
48 = 4 (x + 3)
48 = 4x + 12
36 = 4x
x = 9
Check:
x + 3 = 9 + 3 = 12
12 x 4 = 48