Since area is given by a(x)=10x then,
a.) x=5cm
     a(5) = 10(5)
     a(5) = 50 cm²
    a(6) = 10(6)
    a(6) = 60 cm²
b.) the slope is defined by the equation
     y = mx + b
    where m is the slope and b is the y-intercept
    using the given function, a(x) = 10x, 
     where y in that case is a(x) then we can say that the m=10
   therefore, the slope is 10.
    by inspection, there is no constant term or 'b'. then we can say that b=0
  therefore, y-intercept is zero.