Answer
a) Please see the graph.
b) $400/9$ pounds per square inch
Work Step by Step
a)
Two other points on the curve:
$p=1$
$f = 120\sqrt x$
$f = 120\sqrt 1$
$f = 120*1 = 120$
$(1, 120)$
$x=4$
$f = 120\sqrt x$
$f = 120\sqrt 4$
$f = 120*2 = 240$
$(4,240)$
b)
$f=800$
$800 = 120\sqrt x$
$800/120 = 120\sqrt x/120$
$20/3 = \sqrt x$
$(20/3)^2 = (\sqrt x)^2$
$400/9 =x$