Answer:
Step-by-step explanation:
let speed of Stephen=x mph
speed of Diana=x+4
then
6x+6(x+4)=276
divide by 6
x+x+4=276/6=46
2x=46-4=42
x=42/2=21
Stephen is traveling at 21 mph.
Diana is traveling at 21+4=25 mph.
ok so he is owing his sister 24 and he gives her 15
so 24-15=9
but as an addition expression it will be
x+15=24
x=24-15
x=9