Answer:
1548.66 feet
Explanation:
We can draw a straight line down the middle to form two right triangles
This will split the 70 degree angle into two 35 degree angles
We now have two 90-35-55 right triangles
Now we can use cos(55) * the hypotenuse on both sides to get the distance across the lake
Thus we have:
1200cos(55 = 688.29
1500cos(55 = 860.36
Best of luck