Answer:
x=3
Step-by-step explanation:
A=andy's age
b=belinda's age
3a=11+2b
a+b=-2+2b
wowie
a+b=-2+2b
minus b from both sides
a=b-2
subsitute b-2 for a
3a=11+2b
3(b-2)=11+2b
3b-6=11+2b
minus 2b from both sides
b-6=11
add 6 to both sides
b=17
subsitute
a=b-2
a=17-2
a=15
andy is 15
belinda is 17
Set up a proportion.
75/125 = x/1300
125*10.4=1300
75*10.4=780
x=780
Final answer: 780 students