Let$$f$($x$)=3$x$2+4$xf$($x$)=3$x$2+4$x define the instantaneous rate of change $($in ft$/$minft$/$min$)$ of a car moving along the xx$-$axis. What is the instantaneous rate of change at time $1$min$1$min?

Select one:

a$.$

$10$ft$/$min$10$ft$/$min

b$.$

$7$ft$/$min$7$ft$/$min

c$.$

$3$ft$/$min$3$ft$/$min

d$.$

$4$ft$/$min