a.x=15.75 and y=13.75
b.Weight of large box is 110.25kg and 78.75kg
Weight of small box is 123.75kg and 41.25kg
7x+9y=234_____(1)
5x+3y=120_____(2)
making x the subject for eqn 2
x=120-3y/5_____(3)
substitute x into eqn 2
5(120-3y/5)+3y=120
840-21y+45y=1170
24y=330
y=13.75
put y=13.75 into eqn1
7x+9(13.75)=234
7x=234-123.75
7x=110.25
x=15.75