Rearranging formulas is all about simple algebra rules. Just like when solving for x in an equation, you're just isolating whichever variable you want. I'll work this one out for you and hopefully it'll help, but if you need more explanation, then feel free to comment!
D = ViT + 0.5at² Subtract ViT from both sides
D - ViT = 0.5at² Divide both sides by 0.5t²
[tex]\frac{D - ViT}{0.5t^{2} } = \frac{0.5at^{2} }{0.5t^{2} }[/tex] I wrote this step out a little more to show how your fraction will cancel
[tex]\frac{D - ViT}{0.5t^{2} } [/tex]= a I like to flip these around so the single variable is on the right
a = [tex]\frac{D - ViT}{0.5t^{2} } [/tex]
