-ab + 4a + 3 - (-8ab + 6)......distribute the - thru the parenthesis
-ab + 4a + 3 + 8ab - 6.....now just combine like terms
7ab + 4a - 3 <===
B(t)=50×e^2.5t
e^2.5t = 20
t= ln(20) / 2.5
set B(t)=1000 and solve for t via 1000=50e2.5t
20=e2.5t
ln(20)=2.5t
t=ln(20) / 2.5
9/5 is the answer. Add 1/7 and 1/3 which equals 10/21. Then multiply on both sides by 21/10