(1) 2y×5x(7÷18)-1+3?

and

(2) 45÷28(3x+6y)=

not really sure for number one

1. 1.56y × 3.9x

2. 4.8x + 9.6y

(c, 0) i might be wrong so don't put full faith on my answer

step-by-step explanation:

the original amount doesn't ''re just looking for the time it takes for 1/2 of the substance to we have

(1/2) =)     take the ln   of both sides

ln (1/2)   = )   and we can write

ln(1/2) = ) lne     and lne   = 1     so we have

ln(1/2) = -.1092t     divide both sides by -.1092

t = ln(1/2)/-.1092 = about 6.347 days = about 6.3 days (rounded)