2.5 is in decimal form already.
Box 1 : 3 pencils + 7 pens = total of 10
probability of picking a pen is 7/10
box 2 : 3 pencils + 3 crayons = total of 6
probability of picking a crayon is 3/6 which reduces to 1/2
probability of picking both is (7/10 * 1/2) = 7/20 <==
Substitute x for 0 then solve through pemdas -3(-2) = 6 is true