with what? you need to explain whats going on in order to get the help you need!
Answer:
x = 18
Step-by-step explanation:
I the given triangle, it appears that M and N are the midpoints of the segments BG and BD respectively. If it so, then let us solve it.
By mid segment theorem:
2MN = GD
2(6x - 51) = 114
12x - 102 = 114
12x = 114 + 102
12x = 216
x = 216/12
x = 18
Alright, lets get started.
Suppose the original deck size: width = x feet
the width is one-fourth the length given in question means length = 4 x feet
Means the originally area = 
Now the dimensions are changed.
New dimensions, width = (x + 6)
new length = (4x+10)
So, new area will be = 
the area of the new rectangular deck is 128 ft2 larger than the area of the original deck, means

Subtracting
from both sides

Subtracting 60 from both sides


Dividing 34 in both sides


Means width = 2 feet
Length would be = 4 time width = 4 * 2 = 8 feet
Means dimension of original deck would be = 2 feet and 8 feet :Answer
Hope it will help :)