Answer: 195 Red T-shirts
Explanation:
They initially printed 75 blue t-shirts, so make a proportion (red/blue = red/blue)
8/5 = x/75
Red shirts = x = 120
Then they changed the printing ratio to 4:9 (red to blue)
120/75 needs to now become 4/9 by increasing the blues. Let that equal x
120/(75+x) = 4/9
1080/(75+x) = 4
1080 = (75 + x)(4)
780 = 4x
x = 195