Identify fountain pens sold by shop D

From the provided line graph, locate shop D on the X-axis and identify the value for the triangle symbol (fountain pens). The value is 450.

$\text{Fountain Pens}_D = 450$

Calculate fountain pens sold by shop F

Given the ratio of fountain pens of shop D to shop F is 3:4, we set up the proportion: $\frac{450}{\text{Fountain Pens}_F} = \frac{3}{4}$. Solving for F: $\text{Fountain Pens}_F = \frac{450 \times 4}{3} = 600$.

$\text{Fountain Pens}_F = 600$

Calculate total pens sold by shop F

It is stated that 40% of the total pens sold by shop F are fountain pens. Let $T$ be the total sales: $0.40 \times T = 600$. Thus, $T = \frac{600}{0.4} = 1500$. Wait, checking calculation: $600 / 0.4 = 1500$. Let's re-verify the graph values. The graph shows D fountain pens = 450? Actually, looking at the graph, the triangle for D is at 450. $450/3 = 150$. $150 * 4 = 600$. Then $600 / 0.4 = 1500$.

$T = \frac{600}{0.4} = 1500$