Can anyone help me with this question? Thnks a lot.

Huda and Peiqi went shopping with a sum of money. Huda had $30 more than Peiqi. Huda spent thrice as much money as Peiqi. The amount Peiqi had left was $18 more than what she had spent. Peiqi had twice as much money left as Huda. How much money did Huda have at first?

How to draw model for this question? Answer : 7u = 91 & 91 + 9 =100 answer. How to get 7u?