A garden shop determines the demand function q$=$D$($x$)=2$ x$+400/20$x$+7$ during early summer for tomato plants where q is the number of plants sold per day when the price is x dollars per plant $($a$)$ Find the elasticity. $($b$)$ Find the elasticity when x$=3.($c$)$ At $ $3$ per plant, will a small increase in price cause the total revenue to increase or decrease? $($a$)$ The elasticity is