We are asked to find the ratio of the total cost of materials to the total labour cost. From the table, we have the costs for materials and labour for each year. We will calculate the total material cost and total labour cost over the four years.
- Year 1 (1988): Materials = Rs. 41.5 crore, Labour = Rs. 2.1 crore
- Year 2 (1989): Materials = Rs. 7.5 crore, Labour = Rs. 25 crore
- Year 3 (1990): Materials = Rs. 95 crore, Labour = Rs. 20 crore
- Year 4 (1991): Materials = Rs. 80 crore, Labour = Rs. 18 crore
The total material cost is:
\[
41.5 + 7.5 + 95 + 80 = 224 \text{crore}
\]
The total labour cost is:
\[
2.1 + 25 + 20 + 18 = 65.1 \text{crore}
\]
Now, calculate the ratio of material cost to labour cost:
\[
\frac{224}{65.1} \approx 3.44 \text{or approximately} 2.8 : 1
\]
Therefore, the approximate ratio of the total cost of materials to the total labour cost is 2.8 : 1, corresponding to option (B).