Andre makes a trip to Mexico. He exchanges some dollars for pesos at a rate of $$20 pesos per dollar. While in Mexico, he spends $$9000 pesos. When he returns, he exchanges his pesos for dollars...

Andre makes a trip to Mexico. He exchanges some dollars for pesos at a rate of $$20 pesos per dollar. While in Mexico, he spends $$9000 pesos. When he returns, he exchanges his pesos for dollars (still at $$20 pesos per dollar). He gets back $$110​ the amount he started with. Find how many dollars Andre exchanged for pesos. (If you get stuck, try writing an equation representing Andre’s trip using a variable for the number of dollars he exchanged.)