Answer:
x=10
Step-by-step explanation:
1. substitute y for 10 getting -7x +9(10)=20
2. 9(10)= 90
3. with -7x+90=20 subtract 90 on both sides getting -7x= -70
4. then divide by -7 on both sides getting x=10
5. to check u substitute x with 10 and y with 10 getting -7(10)+9(10)=20. then multiply and add/subtract to get 20=20
