Let
y ----> total salary
x ----> number of television she sells
we have that
Company A
y=90x+8,000 -----> equation 1
Company B
y=50x+8,800 ----> equation 2
Equate both equations
90x+8,000=50x+8,800
solve for x
90x-50x=8,800-8,000
40x=800
x=800/40
x=20
the answer is 20 televisions