You need to evaluate the area of circular disk considering also the maximum error in measurment such that:

`A = pi*(r + dr)^2 = 2903.334 cm^2`

You need to expand binomial such that:

`A = pi*(r^2 + 2r*dr + (dr)^2)`

You need to open the brakets such that:

`A = pi*r^2 + 2pi*r*dr + pi*(dr)^2`

You need to estimate the maximum error in the calculated area such that:

`dA = 2pi*r*dr + pi*(dr)^2`

`dA = pi*(2*30*0.4 + (0.4)^2)`

`dA = pi*(24 + 0.16)` 

`dA ~~ 75.9 cm^2`

Hence, estimating the maximum error in the calculated area yields `dA ~~ 75.9 cm^2` .

b) You need to estimate the percentage error such that:

`(dA)/A = 75.9/2903.334 = 0.026 = 2.6%`

Hence, estimating the the percentage error in measuring the calculated area yields 2.6%.