Explanation:
no reason for an "emergency". we just have to do several things for this one problem, but all of these things are pretty basic.
I understand the garden is a rectangle.
the area is
length × width = 1787.5 m²
length = 2×width - 10
the first step is to solve these 2 equations to get length and width.
the second step is to calculate from there the perimeter.
and the third step is then to divide this perimeter length into pieces of 15 m and determine the remainder, so that we can calculate the price for the fence.
1.
we use the second equation in the first and get
(2×width - 10)×width = 1787.5
2×width² - 10×width = 1787.5
width² - 5×width = 893.75
width² - 5×width - 893.75 = 0
the general solution to such a quadratic equation is
x = (-b ± sqrt(b² - 4ac))/(2a)
in our case
width = x
a = 1
b = -5
c = -893.75
width = (5 ± sqrt(25 - 4×1×-893.75))/(2×1) =
= (5 ± sqrt(25 + 3575))/2 = (5 ± sqrt(3600))/2 =
= (5 ± 60)/2
width1 = (5 + 60)/2 = 65/2 = 32.5 m
width2 = (5 - 60)/2 = -55/2 = -27.5 m
but a negative solution is not applicable to a length calculation, so, width = 32.5 m is our solution.
length = 2×width - 10 = 2×32.5 - 10 = 65 - 10 = 55 m
2.
the perimeter of the garden is then
2×length + 2×width = 2×55 + 2×32.5 = 110 + 65 = 175 m
3.
the cheapest price for the fence is to buy as many bulk order 15m rolls as possible.
175/15 = 11, remainder 10
so, the first approach is to buy 11 bulk order rolls and 10 m individual fence wire.
just a quick check, if buying a 12th bulk order roll would be cheaper than 10 individual meters :
12.5 × 10 = RM125
this is cheaper than RM150 for a whole bulk order roll.
so, we stick with our first approach.
the lowest cost for the fence is
11×150 + 10×12.5 = 1650 + 125 = RM1775