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So, we are given that total cost of polishing the brass tray was \[=Rs.2250\]

We are also given the rate at which the brass tray was polished\[=\dfrac{Rs.20}{10c{{m}^{2}}}\]

Let the area of tray be x.

So, Rs. 20 are spent for \[10c{{m}^{2}}\] to be polished.

Rs. 2250 will be spent for x \[c{{m}^{2}}\] to be polished.

By unitary method, we get,

For 1\[c{{m}^{2}}\], the cost is Rs. 2

So, for \[xc{{m}^{2}}=\dfrac{2250}{2}=1125c{{m}^{2}}\]

Step 2: From the above calculation we get that the area of the parallelogram is 1125\[c{{m}^{2}}\]

Now, let, the length of the base be L cm

& the length of altitude of the parallelogram be Alt. (i.e. 45cm)

So, we know that,

Area of Parallelogram\[=L\times Alt.\]

Or \[L=\dfrac{Area}{Alt.}\] ……………..(1)

So we got area of parallelogram as 1125\[c{{m}^{2}}\]

Altitude=45cm

Step 3: Putting the values in equation (1), we get,

\[L=\dfrac{1125}{45}=25cm\]

So we got the length of the base as 25cm.