please help me I don't know nothing about this I've been sitting here on Brainly for hours and no one is answering

Answer:
7.5 units
Step-by-step explanation:
[tex]\frac{3}{4} = \frac{A}{B} \\\\\frac{3}{4} = \frac{A}{10} \\3(10) = 4A\\7.5 = A[/tex]