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49 centimeters 

a rectangle has a width of 45 centimeters and a perimeter of 188 centimeters. What is the rectangles length?

perimeter p = 188 cm

width w = 45 cm

length l = ? cm

$\begin{array}{rcll} p &=& 2w + 2l \qquad & | \qquad w = 45\qquad p= 188\\ 188 &=& 2 \cdot 45 + 2l \\ 188 &=& 90 + 2l \qquad &| \qquad -90\\ 188-90 &=& 2l \\ 98 &=& 2l \\ 2l &=& 98 \qquad &| \qquad :2\\ l &=& \frac{98}{ 2} \\ l &=& 49 \\ \mathbf{\text{length} }&\mathbf{=}& \mathbf{49\ \text{cm}} \end{array}$