Assign a variable to the amount of trouser material, since that's what you're trying to figure out. Call it x..
So you know that the amount of shirt material he bought is 32x or 1.5x.
The shirt material costs Rs. 50 per meter, and he sells it at a profit of 12%.
That means that his profit per meter is 12% of 50, which is 6.
So the sales price associated with each meter of shirt material is 56.
The trouser material costs Rs. 90 per meter, and he sells it at a profit of 10%.
That means that his profit per meter is 10% of 90, which is 9.
So the sales price associated with each meter of shirt material is 99.
So he bought 1.5x meters of shirt material and sold it at Rs. 56 per meter.
So his total sales of shirt material is 1.5x×56=84x.
And he bought x meters of trouser material and sold it at Rs. 99 per meter.
So his total sales of trouser material is x×99=99x.
So his total sales are 84x+99x=183x.
And we know that his total sales are Rs.36,600.
So let 183x equal to 36600 and solve:
183x=36600.
x=200
Since we defined x to be the amount of trouser material, then that is the answer!