90дм 4мм-8м 34см=

To solve this problem, we need to have all the measurements in the same unit. The most suitable unit in this case is centimeters since we are dealing with measurements that fall into the decimeter, meter, and centimeter scale. Let's convert each measurement into centimeters and then perform the calculation.

• There are 10 centimeters (cm) in a decimeter (dm), so 90 dm equals 90 * 10 cm = 900 cm.
• There are 10 millimeters (mm) in 1 centimeter, so 4 mm equals 4 mm * (1 cm / 10 mm) = 0.4 cm.
• There are 100 centimeters in a meter (m), so 8 m equals 8 * 100 cm = 800 cm.
• 34 cm is already in centimeters.

Now, we can add the centimeter values together and then subtract:

900 cm (90 dm) + 0.4 cm (4 mm) = 900.4 cm 800 cm (8 m) + 34 cm = 834 cm

Now, subtract the second value from the first value:

900.4 cm - 834 cm = 66.4 cm

So, 90дм 4мм - 8м 34см equals 66.4 cm.