In 1 minute the water level rises 0.5m. The area of the base of the smaller pool is 25π m². So the rate is 0.5×25π=12.5π m³/min. The area of the base of the larger pool is 64πm². In 1 minute the water rises h m, which is a rate of 64hπ m³. This must be the same rate as the smaller pool so 64hπ=12.5π.
Therefore h=12.5/64=25/128=0.195m approx.
Note that the ratio of the radii is ⅝, but the ratio of the base areas is ⅝², which is the factor which converts the height of the water in the smaller pool to the height in the larger pool.