Triangle area formula: base*height/2
so, 14*10/2 = 7*10 = 70 sq. in.
-12 + 3x + 2 = 5x - 10 - 8x
-10 + 3x = -3x -10
-10 + 6x = -10
6x = 0
x = 0
Use the Pythagorean theorem.
If x is a hypotenuse, then we have:

If x is a leg, then we have:

Answer: 
New length = 30x110% = 33cm
new width = 20x105% = 21cm
original perimeter = 30x2 + 20x2
= 60 + 40 = 100
new perimeter = 33x2 + 21x2
= 66 + 42 = 108
increase in perimeter = 108-100 = 8
percentage increase = 8/100 x 100% = 8%
Find the z-scores for the two scores in the given interval.

For the score x =391,

.
For the score x = 486,

Now you want the area (proportion of data) under the normal distribution from z = -1 to z = 0. The Empirical Rule says that 68% of the data falls between z = -1 to z = 1. But the curve is symmetrical around the vertical axis at z = 0, so the answer you want is HALF of 68%.