In a square, one pair of opposite sides was made 50% longer and the other pair of opposite sides was made 50% shorter
what percent of the square’s area is the area of the new rectangle?

Sorry, maybe is too late for you, But the answer is:
For example: 4 x 4=16cm² if  one pair of opposite sides was made 50% longer and the other pair of opposite sides was made 50% shorter
It became: 6 x 2=12cm²
12/16=0.75
So, the 75% of the square’s area is the area of the new rectangle.

Step 1: 6x-10=1; step 2: 6x=11