If the graph of the equation 20x + 21y = 420 cuts the coordinate axes at P and Q, then what is the measure of the length (in
units) of PQ?

Correct option is B

Given:
Linear equation = 20x + 21y =420
Formula Used:
Distance = $$\sqrt{(x_2-x_1)^2 +(y_2-y_1)^2 }$$​​
If line cut x-axis , then y=0
Solution:
Lets P be point where it cuts x-axis
Then
20x + 21$$\times$$​0 = 420
x =21
P(21,0)
Now at Q x=0,
20 $$\times$$​0 + 21 y =420
y= 20
Q(0,20)
​$$PQ =\sqrt{(x_2-x_1)^2 +(y_2-y_1)^2 )} \\\ \\=\sqrt{(21-0)^2 +(20 -0)^2 }\\\ \\=√(441+400 )$$​​
=29cm