Question 76768
It might help you if you were to sketch this situation.
Draw a small square centerd inside a larger square.
The inside square represents the main building and you can let its dimensions be x by x feet.
The outside square represents the platform and its dimensions would be (x+70) by (x+70) feet.
Since you know that the area of the platform (outside square) is 102400 sq. ft., you can write the equation for the area of the outside square:
{{{(x+70)*(x+70) = 102400}}} Rewrite this as:
{{{(x+70)^2 = 102400}}} Now take the square root of both sides.
{{{x+70 = 320}}} Subtract 70 from both sides of the equation.
{{{x = 250}}}
So, the main building is 250 by 250 feet.
The platform is (250+70) by (250+70) feet or 320 by 320 feet.