To find the value of R required to make the galvanometer measure up to 40 V, we can use the following formula for a series circuit involving a galvanometer

V = I ( R + r )

R = \(\frac{\text{V}}{\text{I}}\) - r

where R = resistance in series = ?, V = total voltage = 40V, I = current through galvanometer = 20Am = 0.02A and r = internal resistance = 10\(\Omega\)

R = \(\frac{40}{0.02}\) - 10

R = 2000 - 10 = 1990\(\Omega\)