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4)
4 is for the  Library,  6 is for the park,  Police is 5 north up...
Distance of Police from park is by using Pythagoras Theorem:

x^2 =  5^2 + 6^2
x^2 =  25 +36
x^2 =  61    Take the square root of both sides.
x  = square root (61) = 7.81.
x = 7.8 miles  to the nearest tenth.

5)
Since it is a square garden, let the side be = x.
The length of the fence = x + x +x +x = 4x.
Let length of diagonal = d =34.

By Pythagoras theorem.
x^2 + x^2 = d^2.
2x^2 = 34^2.  Divide both sides by 2.

x^2 =  (34 *34) / 2 =  17 * 34,  Use your calculator.

x^2 = 578.        Take square root of both sides.

x =  square root (578)
x = 24.04

Total fence = 4x = 4*24.04 = 96.16.

Total fence = 96 feet to the nearest feet.

Aand b are correctly balanced reactions. they have the same number of atoms in both sides of the reaction