given,

Half of John's money plus 1/5 of Joy's money makes hundred naira 2/3 John's money plus 2/5 of joy's money makes #150

so,

x + y/5 = 100  and 2x/3 + 2y/5 = 150

solving them

we get

x = 37.5 (johns) and y =312.5 (joy's)