Answer:
If it is a straight line then ;
RT= RS+ST
90=(7y+4) + (3y+6)
90 = 10y + 10
10y= 90 – 10
10y = 80
y= 80 / 10
y =8
ST = 3y+6= 3(8)+6= 24 +6 = 30
RS = 7y +4 = 7(8) + 4 = 56 +4 = 60
I hope I helped you^_^
