4 weavers weave 4 mats in 4 days. Therefore, 1 weaver weaves 1 mat in 4 days. If there are 8 weavers, then in 8 days they will weave = $8 \times (8/4) = 16$ mats. (The solution assumes 8 weavers).

Work rate = $\frac{168}{6 \times 7} = 4$ shawls per man-day. 8 men in 5 days $= 8 \times 5 \times 4 = 160$ shawls.

Let the number of boys be $x$, then the number of girls is $(60-x)$. From the question, $x(60-x) + (60-x)x = 1600 \implies 2x(60-x) = 1600 \implies x(60-x) = 800 \implies x^2 - 60x + 800 = 0 \implies (x-40)(x-20) = 0 \implies x = 40$ or $20$.

Price = $72 \times \frac{120}{24} = 360$ rupees.

According to the question, $\frac{40}{200 \times 4 \times 6} = \frac{48}{x \times 3 \times 15} \implies x = 128$ bulbs

Total students = $120 + 30 = 150$. Let the food stock last for $x$ days. $120 \times 45 = 150 \times x \implies x = \frac{120 \times 45}{150} = 36$ days.

171 kg $\times$ $\frac{12}{45} = 45.6$ kg.

According to the question, 12 students $\times$ 7 hours = $x$ students $\times$ 6 hours $\implies x = \frac{12 \times 7}{6} = 14$ students.

According to the question, $5 \times 8 \times 3 = 1 \times 4 \times x \implies 120 = 4x \implies x = 30$ days.

2 laborers $\times$ 8 days = $x$ laborers $\times$ 2 days $\implies x = 8$ laborers. Additional laborers = $8 - 2 = 6$ laborers.

12 dozen = $12 \times 12 = 144$ pens. Price of 144 pens is 720 rupees, so price of 1 pen = $\frac{720}{144} = 5$ rupees. Therefore, price of 25 pens = $25 \times 5 = 125$ rupees.

1 liter = 1000 milliliters. $1000 \text{ ml} = 910 \text{ g}$. Therefore, $700 \text{ ml} = \frac{910}{1000} \times 700 = 637$ grams.

Number of envelopes = $\frac{105}{35} \times 10 = 30$

Number of chairs = $\frac{96}{6 \times 8} \times 18 \times 4 = 144$