Let d represent Dan payment and let g represent Greg payment
"Dan paid three times as much as Greg for his dinner" can be represented as
d= 3g
Number 2
Let x represent the cost of Gym A and Y represent the cost of Gym B
Since Gym B cost twice as much as Gym A
Then y=2x
Number 3
Let d represent Diana's race and let c represent Calorine's race
Diana = 3 x Calorine
d=3c