Plzzz HELP (3 QUESTIONS!!)

6) Which of the following numbers is written in standard notation for 1.31x10^-5?

a) 11,310
b) -11,310
c) .01131
d) .00001131

7) Select the expression written in scientific notation that is equivalent to 4.8 x 10^5-9.7 x 10^4.

a) -4.83x10^9
b) 480,000-97,000
c) 3.83x10^5
d) 0.000048 – 0.00097

8) Select the expression that is equivalent to (4 x 10^3)(5x10^7).

a) 4.5 x 10^3+7
b) (4+5) (10^3+10^7)
c) 4.5 x 10^3x7
d) ( 4 x 5) (10^3+10^7)