Can somebody help me with this. 35 points! :)

Convert the number to decimal form. 12) 312five a) 82 b) 30 c) 410 d) 1560 13) 156eight a) 880 b) 96 c) 164 d) 110 14) 6715eight a) 53,720 b) 3533 c) 117 d) 152

Asource of laser light sends rays ab and ac toward two opposite walls of a hall. the light rays strike the walls at points b and c, as shown below: what is the distance between the walls?

Im so bad at fractions they are not my best math thing to work on